Diamond Star Motors = collaboration between mitsubishi, eagle, plymouth to build the eclipse, talon, laser from 90-99. These cars have a plate in the engine bay stating DSM.
GVR4 assembled in Japan not Illinois like a DSM.
Anyways, about your car. Do all the very basics first. Compression and leak down tests, then boost leak test, then Timing belt with new tensioner, crank seal, cam seals, water pump. If you do not find any significant problems after all that I'd go strait to the ecu one from a "DSM" will run the car fine just switch cases.
Best of luck!