[D13]

Aftermarket compressor brackets are available (on ebay even!) to mount Sandeen style compressors. Factory ones are kind of hard to find and mount either big old compressors or the short-lived R4's. Nova parts work if you have the right generation (there are a couple of different sets of pullies). Crank pulley is bolt on and shows up on ebay now and then, or prtty easy to make (buy a farm store pulley and drill 3 holes...).
For the cab side, you need a good donor, or just do Vintage Air. By time you add up all the parts the may need replacing the V A is not a bad deal.