Almost definitely an open planetary design like the Cusco unit, if it did indeed have a torque split. Seems unlikely though. The Monte Carlo edition came out around the same time as the 3000GT VR-4 (1990 in Japan), which had a 45/55 split planetary differential. Granted, the design was different (diff and VCU are one unit in the 3kgt), but the technology was already in use at Mitsubishi.
Quoting VRausch4:
^ Hatchback Coupler?
IDK.....Perhaps the center diff was a different style? Or maybe they translated the weight distribution wrong, and though it meant torque split?