GMC motors are similar to the Chevy motors, but very few parts interchange. The distributor is an example of what will swap. Intake and exhaust manifolds do not swap.
As Tim says hop up parts for GMC motors are not as common and generally cost more.
I have a GMC 270, which is externally the same as a civilian 302 and like the power the motor makes. I'd love to replace it with a 302.
