Both chassis are very much the same. You should consider this long before you do any engine removal. Ask yourself why you want the M3 engine in the car. I guarantee that you are not going to be happy with the M3 engine even with the 220HP. You really want the car to accelerate better and that is purely dependant on the amount of torque transmitted to the rear tires. Your car with the differential from the same M3 will allow you to accelerate to 60 MPH in the same time. Change your differential, if you enjoy the increased performance, then you can mail me a check for the difference in the time and money that you would have otherwise wasted.