"If it were me".
First, get an accurate assessment of what is missing.
Two major points to keep in mind- the original system was R12, and you'll need to upgrade to a newer refrigerant; AND, most of the original components would need to be replaced anyway with new parts, due to wear and/or incompatibility with the new refrigerant.
The info that
@85_Ranger4x4 posted will help get you to that point. Also be aware that there was factory-installed AC, and dealer-installed AC which had differences between them.
If the truck has missing or destroyed AC parts, going back stock will likely mean tracking down some of the bits and pieces,
and then having to buy more parts as new for the reasons above (compressor, hoses, drier, orifice valve and condenser at minimum, and likely the evaporator too).
At this point, again "if it were me", I'd look to see if any of the aftermarket companies offer a "complete kit" package for a first-gen Ranger. Just google "aftermarket automotive air conditioning" and there will be several companies you can check with. If your truck had factory-installed AC, look for a kit that includes a new original-style evaporator to fit in the original location, and you'll need to determine if you'll need the "mount and drive" components for the compressor. What you won't need, probably, is the AC/heater control head and ducting that's inside the cab.
Hope that this helps, and gives you an idea of other possible options. If you'd like, post some pics of you have, especially the evaporator case on the passenger firewall and the engine compressor mount, and we might can pin down more specifics for you.
Good luck!