I don't know Chevy nomenclature, but if the engine you are referencing is a 350, yes you could. Provided, of course, the '76 'Vette also had a 350 in it. That would be a legal upgrade. What you couldn't do was drop that same motor in a '76 Nova that came from the factory with a 6-banger.
My good buddy, and ex-brother-in-law, owns a 2000 Camero, 350, 6-speed. I think it is the LS1. He wants to drop an LS3 into his car. I didn't think he could out found out I am wrong. One motor of a specific type for a newer motor of the same type - an upgrade. BUT!!! All of the emission controls of the newer motor must stay on; he can't use the stuff that is on his '00 car.
Make sense?