Factory AC (vs aftermarket) - What's needed?

[72malibu]

Hello,

I'm helping my dad get his 75 GMC Gentleman Jim back on the road (second owner since 77). We have a California cab that is being taken to the body shop this week. The original and replacement cabs are AC cabs.

My dad took off most of the AC parts (compressor, condenser, etc.) from his truck years ago and lost them. Of course, both cabs still have the ducts and controls.

The body shop wants to know which direction he's going -- no AC, factory AC, or aftermarket AC.

I'm inclined to think factory AC (partly b/c of the ability to use outside air and because the controls/ducts are already there).

What parts are required to get a factory setup going? Is there a certain compressor or any other parts that are needed? Everything has been removed from the firewall on the new cab for prep/paint, so from the firewall forward we have a blank canvas with the factory AC holes to work with. I believe we have an unbroken upper housing from the new cab and unbroken lower housing from the old cab.

A list of the proper parts (e.g., what compressor, condenser, and any special parts for getting an old system working by today's standards) would be highly appreciated. My dad isn't getting younger and I want for him to enjoy his truck next summer.