To add AC in my 71 142 I obtained info and parts from http://www.vintageair.com/index.htm I used a Sandon 508 compressor, a 12x20x7/8 condensor, a new dryer, and a new expansion valve that I purchased localy from a shop. The compressor can be purchased for 134A, different charging fitting and oil, or for R12. The new condensor and expansion valve will handle both. Volvos back then came out with a York compressor and the Sandon compressor will bolt up to the York bracket with an adaptor, also purchased from Vintage Air or made.

The main thing is to obtain the evaporator and all the under dash stuff from an old car.

I will either use R12 or some alternative refrigerent like Duracool. I could use in theory 134A but it may not cool as well. An electric fan may be added later to improve cooling at low speeds.

Vintage air may refer you to a local dealer who could sell the parts cheaper.
I paid:
Compressor 185
Condensor 117
Expansion Valve 35
Dryer 40

Good luck! I will let you know when I get my AC going.