[BlackSheep01]

Sounds as though it's a blown head gasket. That's cheaper to fix (and less hassle) than replacing the whole motor.
No, the bellhousing from a GM 2.5 won't fit, and even if it would, why would you want to put such a thing in a Dodge?

 

[B10alia]

Welcome to Allpar!
Not sure if the GM motor would even fit under the hood. Displacement doesn't have anything to do with dimensions. For example, the 2.5 used in the K car shared displacement with a Mitsubishi-sourced V6. Totally different engines, totally different eras, and I doubt that the 2.5 V6 was ever offered with the 31TH/A413.
I agree on the head gasket. That was a common failure point of earlier 2.2's and 2.5's. I think there was a running change made to a better head gasket, but I don't know when this was. It's a weekend project that you can do with basic tools. The only concern really is whether or not the head warped. The whole project, assuming you don't need a new head and assuming you do the timing belt at the same time (they tend to break right around 90-120k, and are fairly easy to replace as part of head work) should cost under $200. Even with a head, I doubt it would go much over $600.