It might just be me but i'd keep the Chevelle the way it is. Chevelle can be your race car that you can take out occassionally and let loose and you can drive the camaro whenever you feel like without worrying that something would go wrong. I'm sure your Chevelle has the same problem my dads Camaro did you cant drive it regularly because you'll work the engine to hard staying at a constant speed. My dad had a guy build him an over drive trans with a 4 gear??? not sure about that part so he could simply push a button...problem was that they wouldnt last long.