[vectorit]

I personally have very little experience with AC systems, and the rear air of the old burbs I have always known to be problematic. Mainly the old lines, and the old style refrigerant is pretty much a prohibited class of freon. Sure you could scrounge up some of the old stuff, and you'd probably pay a pretty penny for it to be charged only to have a leakage problem.

I guess if I was in your shoes, I'd check around with the AC retro fit companies like Vintage Air and the like to see if they have idea's on preserving your rear air system.

Wish I could be of more help.