You're kind of asking two questions at once here: 1. What vehicles are compatable to pull A/C parts off of?
And 2. What's needed to convert R12 to R134a?
These two questions need two separate answers.
Answer to question 1: I'm not positive about this. Did the Ranger you pulled parts from have AC? Did the BII already have AC before the engine swap? If the Ranger had AC, it should've had everything you need. The only thing that might be tricky is bolting the condenser to the radiator support, since an 85 BII is a different body style than a 92 Ranger, and might have a different mounting configuration. It doesn't matter if the parts originally came from an R12 system or R134a system, they're still the same parts and will work with either refrigerant.
Answer to question 2: To convert an R12 system to R134a, you need to first obviously get all the R12 out of the system. Change the accumulator and orifice tube with BRAND NEW units only. Try to change out as many of the O-rings as you can. If some are a super big PITA to change, then don't worry about it too much (there shouldn't be any that are hard on a BII/Ranger though, so change them all). Remove the compressor and drain all the old oil out. Add a few ounces of new oil (if any part of the system had R12 with mineral oil in it, use Ester oil. If all parts were originally R134a, you can use PAG 46 oil) Add the rest of the oil to the new accumulator. Install all the other components, install the adaptor fittings on the service ports. Evacuate the system and check for leaks, and recharge. Done.