Caliper Spacers:  First and foremost, a set of spacers are needed to widen the calipers.  The calipers need to be widened by the same amount that the rotor is wider than OEM.  We are talking about replacing the 1/2" solid rotor with a 3/4" vented rotor so we need to use 1/4" spacers to widen the calipers.

Note that, if you happen to be upgrading a Series 1 E-Type, the first thing you will have to do is upgrade to a later caliper design.  The Series 1-1/2, 2, and 3 E-Type and XJ6/12/-S inboard rear brake calipers are all reportedly similar and will fit the Series 1 E-Type with only minor fiddling.

This is a picture of one half of a caliper -- the inboard half of the left side caliper, to be precise.  The mating surfaces on either side at the top of the picture is where the spacers go.  To make things really pretty, you need to cut out your spacers to the same shape as those mating surfaces so it looks really smooth when it goes together.  However, for practical purposes, the cutout doesn't really need to be so precise.  You should, however, make sure the spacer is at least as large as the mating surface of the caliper to give the mating joint a solid "footprint".

Since those mating surfaces are less than an inch wide, you can use rectangular bar stock that is one inch wide and the desired thickness to make your spacers from.  1" x 1/4" rectangular bar stock is readily available.  You can also make the spacers from 1/8" or even 1/16" stock; just make more of them and stack them up.

Drill the two bolt holes first, then use the bolts to hold the spacer against the caliper while you mark out the outline.  If it's of any help to you, you can set one half of a caliper on a flatbed scanner, prop it up so the mating surface is sitting flat against the glass, and scan yourself an actual-size image of the mating face.  You could, for example, print it on a sheet of paper, tape it down to your piece of steel, and use a center punch to mark the locations of the holes.

On the edge facing the rotor, you need to make sure the edge of the spacer doesn't interfere with the rotor itself.  The end of each spacer pointing towards the pad retaining pins can be left quite long, just make sure it doesn't interfere with the installation of the pins -- but they are more than 1/4" away.  The spacer cannot possibly interfere with the pads themselves, since the spacer is 1/2" narrower than the rotor.  The outer end on the end with the handbrake calipers must be short enough to avoid interfering with the bronze fork installation; the outer end on the other end (lower end in the car) can be almost any length.

The spacer edge that is critical, believe it or not, is the upper edge in this picture, the one facing away from the rotor, the one facing forward in the car -- especially the spacer on the lower end of the caliper as it sits in the car, the one on the non-handbrake end of the caliper.  Especially the one on the right side caliper.  This surface just barely clears when removing or installing the caliper in the subframe.  Make sure to grind it down to flush with the outer surface of the caliper itself in this area.

Palm happened to have some 1/4" steel plate laying around (doesn't everybody?) so there was no need to purchase any bar stock.  The stuff was good 'n rusty, so a little steel wool was in order.  The completed spacers looked like this:

These spacers don't cost any money to speak of, but they do take some time to drill and cut out.

Caliper Bolts:  The next items needed are the 3/8"-24 bolts to hold the calipers together.  Don't use the originals, they're too short and you want to make sure to engage enough threads to hold the halves together securely.  The original bolts are 2-1/8" long -- but they're actually a bit too short to begin with!  They could have been a quarter of an inch longer originally before you even start talking about spacing the caliper.  For 1/4" spacers, 2-1/2" length would be good.

Go with Grade 8 or "alloy steel" bolts; this is not a place for scrimping on cheap bolts.  It doesn't really matter what type heads you find; socket head allen bolts might look cool!  The original bolts have no locking plates or lockwire because they are fairly long bolts; the length will provide enough "stretch" when torqued to ensure they won't vibrate loose.  You can drill holes in the heads for lockwire if you're that kinda guy.  Be sure to apply anti-seize compound to the bolt threads when assembling.

Bridge Pipes:  You're going to need to do something about the bridge pipes, the pipes that connects the two halves of each caliper.  They obviously are configured for a particular spacing between the fittings, and you've just increased that spacing by the thickness of the spacer.  Since the spacers are only 1/4", you can actually bend the original tubes just a bit and make them fit.

In this picture, the upper bridge pipe is the original shape.  The lower one has been suitably bent to fit a caliper with 1/4" spacers in it.  Note that the bending needs to not only address the additional distance between the ports, but it also must result in a configuration that will clear the corners of the caliper and the handbrake pivot pins.  It is advisable to have a caliper assembled, with spacers, on hand when doing this bending.

Brake Pad Retention Pins:  The pins that hold the main caliper pads in place have to be replaced because the originals are now too short by the thickness of the spacer.  This is a really easy job; in fact, there are four ideas presented here.  The first is the way Palm went, which was to make new pins from really long 1/4" bolts.  The original pins are 2-5/8" long under the head, so the 1/4" bolts need to have a smooth shank at least that long plus the 1/4" thickness of the spacer.  Palm bought 4" long 1/4" hex head Grade Nil (there's no need for strength here) bolts at Wal-Mart, where they come two to a pack (with nuts!) for less than a buck.  Saw the threaded end off, then chuck the rest of the bolt up in a lathe or drill and grind the head down to something that looks nice.  Note that of the four holes these pins must fit through in each caliper, one is recessed, so the head must be ground down at least far enough to fit into that recessed hole.  Finally, drill a 1/16" hole for the clip the same distance from the headed end as on the original, and you're done.  Can be done in just a few minutes.

In this picture, the upper pin is the original.  The middle one is the longer one made from a bolt; at the bottom is the type bolt it was made from.

Another idea is to purchase a length of 1/4" steel rod (available at hardware stores), cut it into suitable lengths, and drill two holes in each for clips to hold them in place.  You need the second hole to make up for the lack of a head.  Drill the two holes located so that the clips will be just inside the openings in the calipers, with enough space to allow it to rattle a little.  The prime disadvantage of this method is that you're going to have to find four more clips!  The advantage, though, is that once the clips are removed, the pins can come out either direction.

Yet another solution is to buy some genuine Girling brake pad retention pins that happen to be longer.  They're not too hard to find, either -- they're about 8 feet away at the other end of the same car!  Yes, the pins used at the front end of the XJ will fit perfectly; they are part number 12798.

After Palm thought about things a little more, he decided that installing the clips in the vicinity of the caliper dust boots -- where they were originally -- may not be wise, even though the problem of these clips damaging the boots appears to be more of a concern on the front brakes.  It is easy enough to drill new 1/16" holes out at the end of the pins and put the retaining clips outside the calipers.

If you concur with this notion, the idea of using steel rod and two clips goes away because one end of one pin in each caliper fits into a recessed hole, and the clip won't fit.  It does bring us to a fourth possibility, though, and that is to purchase generic "clevis pins" in 1/4" x 3.00" size.  The hole for the clip is already in the correct spot to be outside the caliper, no drilling required!  They're cheap, too, apparently; here's a pack of 25.  Here's a pack of 5 in 18-8 stainless steel.

Handbrake Caliper Links:  A concern with using the handbrake calipers with a thicker disc is the link that connects the two handbrake caliper halves.  This is part of the adjuster; one end is threaded so the adjuster can operate by turning a threaded cogwheel on it, and the other end is pinned so it cannot rotate.  It looks kinda like a long screw with a slotted head.  When the calipers get 1/4" farther apart, these links needs to be 1/4" longer -- or do they?

The adjustment range on the existing links does seem to be long enough to deal with 1/4" spacers -- but just barely.  To properly assemble the handbrake system, the adjusters need to be adjusted quite a bit loose and the bronze fork tines configured to hold the pads away from the rotor.  When assembled, the handbrake levers should be manipulated back and forth repeatedly until the adjusters pull the pads against the rotor and preload the bronze fork tines.  To assemble with 1/4" spacers and new handbrake pads, the adjuster needs to be out on its last thread when installed!  But that's OK, because adjusting it to pull the pads against the rotor will thread it in about another 2 or 3 turns, providing enough thread engagement to hold it securely under load.

If you prefer, it should be easy enough to make replacement links; both are right hand thread (the two adjusters are not mirror image of each other, they are in fact the same part flipped over, and everything except the caliper itself is interchangeable right to left side).  A socket-head alloy steel screw would be good; chuck it up in a lathe (or a drill) and grind the underside of the head to form a ball shape like the original, and then use a hacksaw to cut a slot in the top for the cotter pin.

Handbrake Pivot Pin Locking Plates and Retraction Plates:  The handbrake calipers pivot around a pair of pins that are threaded into the main rear caliper.  There is a bronze "retraction plate" (which Jaguar owners commonly call a "bronze fork") part number 64328290 or 9750 that is secured under the heads of these pins along with a locking tab part number 9751 to make sure the pivot pins don't back out.

The purpose of the retraction plate is to pull the handbrake pads back off the rotor surface just a bit when the handbrake is released so that friction and wear are minimized.  As the pads wear, the tines of the fork deform to follow along and continue retracting the pads just a bit.  If the pads are renewed, the tines must be bent back to their original position or the retraction plate replaced with new.

This is all well and good -- except that we've just widened the caliper with 1/4" spacers, so neither the retraction plate nor the lock tab will fit any more!  We must figure out how to achieve both objectives, locking the pivot pins and retracting the handbrake pads, with our widened calipers.  These functions tend to be intertwined, so both are discussed together here.

Ideally, the same thickness of stuff should be stacked under the heads of those pivot pins so they are neither threaded in too far nor holding on with insufficent thread engagement.

You can, in fact, just saw the bronze fork in half and bolt it in, and everything will appear to work fine.  The only problem is, you might as well just leave the fork out.  The fork halves will just pivot around the pivot pins and the pads will simply ride against the rotor.  The handbrake pads will wear more quickly.  It will also result in heat buildup while driving, possibly charring the handbrake pads.  It's a better idea to do this job right.

Idea 1:  Brazed Retraction Plates:  Jan Wikström cut his bronze forks in half and brazed in a section to widen them.  This is a good plan, and the middle section you're adding doesn't need to be bronze; it can be steel or brass or whatever's laying around.  The pivot pin holes in the bronze forks are 1-5/8" apart to begin with, and since you're adding 1/4" spacers between caliper halves they'll need to be 1-7/8" apart when you're done brazing them back together.

You still have to lock the pins in place.  One idea is to drill a 1/16" hole crossways through the head of each pivot pin and apply lockwire.  This will work but it might be a bit of a challenge without a drill press, and you don't want to screw up that pin because you'll have to wait on shipping to get a replacement.  It's really easy with a drill press, though, so just taking your pins to a machine shop and asking them to make lockwire holes shouldn't cost much.  Use some flat washers so the heads aren't tightening down directly on the bronze fork.

You can also try to find the type of tab washers that are used on individual screws.  Seastrom makes one that looks like it'd work -- but I certainly wouldn't expect you to pay those prices.  You'd need to find a retailer that sells them individually.  You need four, and next time you rebuild these brakes you'll need another four.

You could also just purchase the OEM locking tabs part number 9751, and cut each one into three pieces.  Throw the center section away and figure out how to install the end pieces bending some tabs down to hold the locking tab still and other tabs up to lock the pins.

Another idea, obviously, is to make your own locking plates.  This isn't too difficult, but it will take some patient cutting and trimming -- and next time you have this thing apart, you'll have to make new ones!

Finally, you may also be able to purchase locking plates with the correct 1-7/8" hole spacing from the Terry's Jaguar Parts kit separately since presumably previous purchasers of their kits will need a new set whenever they do brake work.

Idea # 2:  Lipped Retention Plates:  Palm used an idea stolen from the picture of the Terry's Jaguar Parts kit.  Their idea is to use a locking plate with an edge folded down to prevent a bisected pair of retraction plate halves from rotating around the pivot pins.  The fork halves cannot turn because they run into this lip.  Palm fabricated such a locking plate -- but he didn't provide any locking tabs on it!  Instead, he drilled the heads of the pins for locking wire (Palm has a drill press).  This way, each time the assembly comes apart new lockwire can be used but the "lipped retention plate" can be reused over and over.

Here is a diagram for making this Bronze Fork Retention Plate.  It's presented as a PDF file so you can easily print it out; if all goes well, it'll print actual size.  Make a pair of these plates out of some sheet steel that the pivot pins can be tightened down onto without deforming it.  Precision isn't critical; you can see in the photo that Palm's were handmade, and they worked fine.  You can add locking tabs to the design if you want.

As mentioned above, another idea might be to simply purchase a pair of the locking plates from Terry's Jaguar.  You might opt to simply cut the locking tabs off and use lockwire to secure the pivot pins so you never have to buy another pair of the locking plates.

Assembling with these lipped retention plates requires explanation.  Obviously, cut your bronze forks in half; cutting new bronze forks in half is recommended, as the bronze tines get bent as the handbrake pads wear and can only get bent back to the new position so many times before they just snap off.  Install the bronze fork halves first, making sure that the tines of each half of the bronze fork are correctly inserted into the holes in the handbrake caliper and that the handbrake adjuster is backed out far enough that neither handbrake pad contacts the disc.  Position the plate on top of the bronze fork halves with the lip positioned behind the split center section of the bronze fork.  Install the pivot pins (flat washers are recommended to protect your homemade plate) finger tight.  With the parts so assembled, operate the lever on the handbrake back and forth to get the adjuster to begin taking up the slack and applying a load on the tines of the bronze fork halves.  As they get loaded, the bronze fork halves will try to rotate around the pivot pins until they jam against the lip on your retention plate.  When the bronze fork halves have been so loaded -- hopefully still without the pads contacting the rotor -- tighten the pivot pins down securely and bend the locking tabs or apply lockwire.  Then continue to operate the handbrake lever until the adjuster has taken up all the slack and the handbrake pads are positioned very near the rotor.  Check that the tines on the bronze fork halves are pulling them a tiny bit away from the rotor whenever the lever is released.

Don't get carried away operating those handbrake levers by hand.  Just get one click per swing.  When really loose, it's possible to move it far enough to get two clicks, but it's also possible to get the clicker to pop out of place inside the adjuster -- meaning you'd have to take the thing back out and open it up again!  You don't wanna do that, I'm sure.

Idea #3:  Pinned Retraction Plate Halves:  Brian Schreurs reviewed the assembly of a 6.0 litre TWR:  "On this car, they sliced the fork in half and secured the halves by drilling small holes through the fork and into the caliper, and holding them down with cap screws."  This is a good story, but it's not readily apparent how it would work.  There is no underlying structure in the caliper to drill into; the area under the bronze fork between the pivot pins spans open air.

Here's an idea that will work, though:  Make plates of the same layout as the lipped retention plate only without the lip, which makes it really simple; it's just a straight flat piece of metal with two holes drilled in it.  Assemble the handbrakes with the tines of the bronze forks engaged with the pads, but don't take up the slack in the self-adjusters yet.  Drill two holes through each plate, one into each of the bronze fork halves.  Use screws to secure the fork halves to the plates.  Make sure your screws can't come loose.

There are at least three ideas for those screws.  First idea:  You could drill small holes and then take the plates and bronze forks back apart, being careful to mark them so they go back the same way.  Tap the holes in the bronze forks and enlarge the holes in the plates to fit the same size screws.  Put it all back together, using screws that have safety wire holes in the heads.  Safety wire these screws to the heads of the pivot pins right next to them.

Second idea:  Drill holes sized for screws, say #6 or #8, clear through plate and fork, being careful that your holes are far enough away from the caliper to allow room for nuts.  Install screws with self-locking nuts on the back side.  You want all-metal self-locking nuts; things get too hot here for nyloc inserts.  Safety wire the two pivot pins to each other; the self-locking nuts will ensure the smaller screws don't come loose.  This scheme has the advantage that the brakes don't have to come back apart to drill and tap.  The disadvantage is you have to get those nuts onto the back side of the screws and get a wrench on them to tighten them down.  Or you could take the handbrakes apart far enough to tighten the nuts down, then reassemble.

Third idea:  Use pop rivets instead of screws.  That makes it really easy:  Drill, pop, you're done.  It might be a good idea to use steel pop rivets instead of aluminum; I dunno how the aluminum ones would hold up to the stresses here.  If you ever need to rebuild these brakes in the future, just grind the heads off the rivets and reassemble with new bronze forks and new rivets.

The Redneck Solution:  At least one vented rotor kit omitted any parts necessary to fit the bronze forks to the widened caliper.  When asked why, they answered "It is presumed that the owner will simply throw the handbrake calipers away."  Please don't be like that.  Perhaps you've never experienced a brake failure, but if you ever do it'll make a believer out of you.