now if you really wanted to do something special.... Take the entire powertrain from a new cobalt SS Turbo.
The 4 cylinder engine is light, comes with a manual gearbox, and has more power and torque than both V6's you are looking at (260hp). (the cobalt gets over 30mpg highway with that engine too)
With the weight reduction you would get by going to that engine, the car would handle amazingly well. The wide track of a grand prix with significantly less weight from a smaller gearbox and engine. It's also really easy to turn up the boost on that engine to well over 300hp. (people have done it already reliably)
