The early 123 automatic climate control system (through'79) did indeed have a Chrysler servo system and I think there are some vacuum components. This is an EXTREMELY difficult to rebuild climate control system.

That said, this has little to do with the compressor, only the climate control (automatic temperature control) function. I'm pretty sure that your car has a two cylinder York type compressor. You do not state what your goal in "upgrading" is. Regardless of the compressor, your biggest problem will most likely be the servo climate control system.

Assuming that you want to change from the York compressor so that you don't have to use R12 would be false economy. Your York is probably in good shape and if not, a quality rebuilt can be had for $100. That's very cheap in "compressor dollars." Since R12 prices are going down, you can get it for about $15 a pound or so. To convert to a different compressor would cost hundreds and hundreds of dollars. Not an economical endeavor just to replace $15 refrigerant with $6 refrigerant.

The refrigerant, even R12 is probably, by far, the cheapest component in your a/c system, certainly in your Chrysler Servo control system.

Good luck,