Check out the 8-1/4 rear end in that truck. My son's came with 3.91 SG from the factory. But you'll have to deal with the odd bolt pattern.
His is a 98 Std Cab, Std Bed, Dakota R/T, 5.9 Magnum. He runs 13.7's in the quarter. it weighs about 4000 lbs. Bolt-ons are M1 Intake, larger throttle...