need a lesson in A/C

Change to R-134A today? Don't you guys know it is outlawed in many countries and soon in the U.S.? I changed all my vehicles to Duracool, even my 2002 when the compressor failed. Works slightly better than R-12. But, if the EPA is watching, legally you must first convert to R-134A, even though that is very bad for the environment (climate change gas).

The only thing "old" about your design is the heavy compressor. Otherwise, nothing much has changed in AC, other than a parallel-flow condenser is 30% more efficient, but those existed in the 1960's. Your RV-2 compressor is very dependable, just a beast. For retrofit, a smaller Sanden is best choice, and you can get brackets for your SB (Bouchillon, etc). I wouldn't waste new refrigerant on those old hoses. If you have an AC crimper like me, it is easy, or buy Oeticker hose clamps on ebay and crimp w/ a nail puller, or even Breeze screw clamps work. Can also take to a hydraulic hose shop to refit.

If you don't have a good vacuum source, you can do "good enough" by sucking a vacuum w/ your intake manifold, switch to a hand vacuum pump and try to get it to at least 20" Hg, sit for hours to out-gas any water, fill w/ Duracool or Enviro-safe, then vent a little off to blow out any residual air or vapor. You can't legally vent hydrocarbon refrigerants per EPA, though that is what is in many hair-spray cans and cow farts. Also, first read the foolish worries about "explosive" HC refrigerant from non-tech people (zip it, I'm an engineer who studied combustion in grad school). No fires in millions of cars yet from that. If using R-134A, better to use PAO 68 oil since PAG absorbs moisture to form corrosive acids, in which case you better pull a very hard vacuum first.