It doesn't have to have the same chassis strictly speaking, although it certainly simplifies things (more like legos than custom motor mounts), it's just that the MY of the vehicle chassis that the engine and junk is going into must be the same or less than the certified engine/emissions package. That way people can't put a 75 engine into an 80 car to avoid smog. I think the transmission also has to be the same as an existing certified configuration technically, but it's not something I've ever heard of being enforced. I always thought dropping one of those 8L GM engines in a rusty compact would be cool, if it could be made to fit. Maybe cut the car in half then weld it up around the engine/trans in it's own subframe or something?
