I did this backwards.... I put a 5.2 (318) flywheel on a 3.9 in my 87 dakota so I could use a NV3500 transmission..... On another site, I have seen others do exactly what you are doing, and it worked. But keep in mind the NV2500 trans, is weak.
A little off base, but with a 87-90 dakota, your biggest problem is going to get the motor to clear the radiator. In short, I believe there are 3 ways.....
1. As Shelby did with the 89 shelby dakota's, make a special crossmember and move the motor, trans back. Then use pusher electric fans in front of the radiator.
2. Use a magnum serpentine belt system, along with pusher fans..... This is what I am doing on mine.
3. Swap out the front end for a 91-96.... Dodge moved the radiator about 4 in forward to provide clearance.
Below is a picture of a 3.9, and the factory radiator. Figure the V8 will add 4.5 in. to the length of the V6....
View attachment 1715603734
View attachment 1715603735
