Best thing would be an aftermarket kit from one of the vintage a/c vendors (Old Air, Vintage Air, etc.). Which would mean a "hang down" evaporator/fan assy under-dash. With a Sanden compressor, of course. Using R-134a gas and oil.
I just put air in my 63 Belvedere beater. Got it from Speedway Motors, Vintage Air .
With engine brackets out sourced from another vendor the cost was about $1400 all done.
Mine was heat and air. Air alone would cost less.Works great in Nevada's 100* + weather.