R12 vs 134a

This isn't about an a body but very well could be.
Adding factory AC to my 85 truck, have most of the under dash parts from a junker. I plan to rebuild the plenum box before I put it in.
I don't know if something like this exists but is there any difference between evaporator used with different types of freon?
Same q applying to the receiver drier. And condenser.
PS////still looking for AC compressor mount brackets for a /6