Converting a Series III Air-conditioner to R134a

In servicing my recently acquired 1982 Series III XJ6, I noticed the Air-conditioning compressor (GM Harrison A-6) was throwing oil thru the front seal (although it still worked great.) Hot weather coming on, I found a replacement at Western Auto (Parts America) for $59.95 with core exchange. A friend of mine is liscensed for R12 removal and has the equipment. He drained my system, and me and my dad went to work. We removed the compressor and replaced it with a remanufactured GM A-6 designed for the temperature/heat fuse. (Please note I had no leaks on the system.) We changed the accumulator/dryer-and changed only the o-rings we had disturbed. (Some techs say you must replace all the o-rings in the system and the expansion valve as well. The GM shop manual on the A-6 compressor said to replace ONLY those o-rings which were disturbed and expansion valve replacement was not necessary unless the previous compressior had failed-and my system was working well, even though it was running out of oil.) We then pulled a vacuum on the system down to 28.5 " of mercury for 45 minutes. We added 8 oz of Ester oil to the new compressor. A tech at http://www.britishcarparts.com informed me the original R12 charge was 3.4 lbs (the original tag indicating the R12 charge was gone from my bonnet), so we first attempted an 80% charge which didn't cool very well, then a 90% charge which resulted in a vent temperature of 55 degrees farenheight on the road and 60 degrees farenheight at idle speed with an ambient temperature of 90 to 100 farenheight. I then discovered a leak in my new system. We failed to be certain the charge valves were tight and the high-side valve was leaking. We discharged what little R134a was in the system, put in new valves and new quick connect R134a conversions and pulled a vacuum on the system to 28.5 " of mercury for 4 hours just to be sure there was no leak again. This time, with a thermometer in the vent, we began to charge the system. At 36 ounces, about 65% charge of the original 3.4 lbs (for the R12 system), the temperature in the vents reached 38 degrees farenheight with an ambient temperature of 90 - 90 degrees. On occasion the temperature in the vents goes down around 32 degrees farenheight. The R134a system has worked great for weeks now and it's Hot summer time in West Texas 90 to 100+ degree (farenheight) days. The system cools as good or better than the original R12 system did, and I am happy and cool. Total cost was about $225.00. (My friend donated the labor and equipment necessary for R12 removal in exchange for the R12 in the system.)