I wouldn't go with trying to fit a GM hybrid drive in because the modern ones are pretty complex. The sensors and computers would make it a nightmare.
Let me suggest contacting some of the
electric vehicle groups. They'll be a wealth of information and experience to help on the project.
Just curious, how comfortable are you with high energy hydraulics? This could give you a regenerative braking and acceleration assist that would make the car both efficient and a sleeper on the street with rubber burning performance.
Bob Wilson