the Impala SS in the mid 90s had a RWD LT1, and then the newer ones used a supercharged V6 on a FWD platform, and the current generation uses a very small V8 ina FWD configuration and that same setup is also used on the current gen Monte Carlo SS.
that aside, i would say that a 3000GT is not the car to be doing this with. a friend of a friend has a 3000GT that he is rebuilding, and it seems as if the motor thats in there barely fits, so i dont really see how you’re going to stuff a V8 in there without a TON of custom work and a lot of money. im guessing you would have to modify the suspension quite heavily because the V8 and its transmission s gonna be a decent bit heavier than whats in there now. you really would have yo know your stuff to pull it off too.