well it depends
dealer installed a/c?
dealer and factory installed a/c will be totally different from each other
dealer installed will have aftermarket a/c duct vents in the dash and the compressor wont be a harrison black colored one that is so common on GM vehicles
if one car has dealer and the other has factory then they wont interchange
also the dealer a/c wont have an a/c heater box assembly like harrison factory installed ones are
will be the smaller a/c delete heater box, and the a/c lines will run through the firewall, and not through the heater box.
ebay, chevy nova forums sites, and craigslist.org are ways to find parts you may need, i should have also if it is the old long style harrison compressor, and sbc engine.