i just swapped the whole engine in because it's much more simple and i had it there. i did the same with the harness. if you just swap the intake manifold, you'll at least need an '84+ head because the earlier style heads didn't have the different studs for the injection manifold, the knock sensor, and all the wiring and ecu. i think the gear transfercases were all the same from 79 to whenever they changed to chain drive. i'm not sure though. you could probly just look here on marlin's site and see.
