3.9 Liter V6 Swap

Ive had several Dakotas both 318 and 3.9. The 3.9 is a long lasting engine for sure, many with over 250K and still going.
The biggest problem with them is being an "odd fire" V6 they are harder on timing chains than the V8, which takes the same chain and gears.
same labor as a V8 to change, they arent terrible to do.
BUT I must say that my 318 Dakotas have ALOT more power AND get the same (or better) mileage. and the same longevity with the same amount of care given to each.
My 90 (non Magnum) was the best on fuel MPG if that is what you are after, 16 (worst) 20 (best) my 94 was the peppiest, and my current 99 is the doggiest. My 94 and 99 seem to both top out on MPG at 17/ on the 99 it seems like I have to put my foot "thru the floor" to get it to go. my 94 pulled my popup (same camper) easier it seemed, than the 99. all my v6 Dakotas were 3.55 geared with the "A500" trans (42/44, RH/RE) so no variable there.
my 96 318 Dakota (only 4wd Dakota of the bunch) with 3.91 gears (only one of my 6 Dakotas to have had that ratio) can get 17 on summer blend gas in combo mixed driving. normally it's about 15 to 15-1/2 esp in the winter. My 2wd 318 Dakotas were slightly better. especially my 93 of which I converted to a NV3500 5 speed stick. That truck got an easy 20, and went like a bat outta He11.
You cant get these series trucks off teh showroom floor anymore and I like them overall much better than anything newer, so I take what I can get. V6 or V8. I look 1st for good body and frame and take whatever mechanicals come with the truck at that point. I miss the 93 the most, with its V8/stick and Id still have it if it hadnt been so badly crashed.... I put 72k miles on that truck for very little money. definitely got my moneys worth. the only one of the bunch that I am sorry I bought is the 99.
It has had alot more mechanical issues in a short time than any of my square bodys. and it was the lowest mile "when I got it" of any of them. Came with the biggest pile of reciepts showing it was maintained by the PO. alot of my repairs have been "redo's" of repairs he had paid someone else to do. and some things that you would have thought tehy would have done "while they were in there" but didn't. but I am so behind the 8 ball on the 99 that I have no choice but to run the wheels off of it cuz I surely wont come close to getting what I have into it back out. The rest I drove the wheels off, because I liked them, instead.
But all that said, no, I would not swap/retrofit a 3.9 into anything.