If your not intending on using the efi, and will go with a carb, any Dakota truck would probably work. I'd have to take a look under that 4 door truck and see what the frame looks like, and if the drop will be in a good position for whatever cab/body you intend on putting on it.

As far as the V6 to V8 motor, the mounting pads on a Dakota bolt to the frame and those brackets are engine specific. 3.9 fits a 3.9, a 318 fits a 318, and the 4.7 fits a 4.7. How they might interchange between motors is anyone's guess. These days, all the electronics are motor specific, so swapping from, say, a 4.7 to a 318 means you get to swap the complete wiring harness and computer and you better have everything that matches the motor and trans (that came out of a Dakota, or the wiring will be wrong) you want to use. Weather the motor mounts are the same or not becomes a minor issue, you would probably use the ones attached to the motor you pulled out of a Dakota, and they will probably bolt to the frame.

The next thought on the motor mount is will the engine will remain in its original location as a hot rod is built? With my coupe, I moved the drive train back 7". Once you move the motor, whatever was there originally is a pretty mute point. In my case, I just added a 1/4" plate and moved the motor brackets and trans crossmember back the required distance (used what fit the motor and trans and adapted it to the frame where I wanted them to sit).

If you have the ability to swap a frame from one vehicle to something entirely different, motor mounts should be just another step in the frame swap process. Use whatever mounting brackets fit on the motor of choice, and modify them to fit the frame. Gene