I've searched and realize that there are two different ECU's for the 1995 and the 1997. If I purchase a 1995 420A will I need the 1995 ECU to run it properly in a 1997 GS?
If you are using a 1995 Motor, no you will not need to swap out your ecu to a 95 ecu, as long as your car is a 97. The ecu has to match the same year that your car is, not the same year your motor is.