The Admiral is a factory A/C car but I swapped to a Sanden type compressor using a kit available from Vintage air and changed to R134.
Now I don't have to lean into the gas when the old V2 compressor kicks in.
Original in mine. If your question is about what you might want to use in your, check into Vintage Air. They do a lot of rods and other cars. My uncle used them to put an AC in his '65 Mustang.