Even so, the vast majority of aftermarket tips are cheap chrome plated steel that will look like hell in only a short time.  J. C. Whitney sells stainless steel tips in various sizes with either a straight-cut tip or an angle-cut tip.  Below is what the angle-cut tips (catalog number 12xx0952Y) look like on the author's '83.

 Note that the angle of the pipe tip itself is due to the stock Jaguar muffler having a bend right at the outlet.  The bend is actually steeper than that, but by sliding the tips all the way on and tightening the screws down onto the bend itself the tips can be closer to horizontal than the muffler outlet.  The only way you're gonna get the tips horizontal, though, is by modifying or replacing the stock mufflers.