The 5.9L Cummins is much too big and heavy for a YJ frame. Hell, it's too heavy for pickup frames unless they're reinforced and have heavier springs. Also, it has way too much power (torque) for even a D44 and Ford 9-inch. My 1-ton Dodge truck handles the torque of it's Cummins, but it has a Dana 70 rear diff and a Dana 60 front diff. It also has an NP205 T-case.

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.