95 Riv

Hello everyone. I just bought a 95 Riviera S\C , this is my first one. Unfortunately, it is in need of an engine. I owned a 99 Pontiac GP GTP, and sold it, regretfully. Hopefully this Buick will have the same performance the Pontiac did, I know it is much heavier.
Well to the point, while looking for an engine. Is it possible to put a series II engine in, with minimal to no problems, or do I need to find another out of a 95 ? Or, maybe even out of a Pontiac?
Any insight will be appreciated, thanks.