I rebuilt my 65 air last year for 134 and might answer a few of your questions. First off I am still working on mine so not sure the final outcome of R12 vs 134. I have read everything from works great to no way. I decided to go with 134 because I plan to keep and the R12 will only get more expensive and hard to get. My conversion was done by Classic Auto Air in Tampa, FL. The only reason I went with them over the Texas people was they seemed alot more helpful on the phone. Have been very satisfied with Classic. All that they need is your drier and suction throttle valve. They cut and re-weld the drier and it looks great. No visual change to the stv. Cost is around $160. You also need to clean the entire system with a cleaner designed for ac (I got some at a NAPA store - expensive, around $25 for small can). I replaced all hoses so the only thing to "flush" was condensor, compressor, and evaporator. The problem I still have with mine is a small leak in the expansion valve. I have a new one but it is no fun to get to now with the engine and eveything else back in the car. Also I read an article recently talking about the importance of the drier so I would suggest doing something with it whether you convert to 134 or not. Hope this helps, Don H.