If only I could weld....I'm dreaming of a V6 powered RWD Aveo. LOL.
I'd go V8 But a Buick 3.8 is a cool little motor with plenty of power for its compact size.
One from a late model turbo regal would be nice. With some welding you could make a rear axle from an old 70's chevy monza work,using the torque arm system to keep the axle in place, the way they did in those cars. The floor will need a little cutting in the tunnel area for the transmission. The cutting and welding would be a massive task, Otherwise, looks like its totally possible.....