The 3/4 ton trucks have a thicker (roughly 1/4" thick instead of 3/16") and/or bigger C channel (about 7" vs. 6") frame. Spring eye bolts and other suspension parts are larger on heavier duty trucks also. You can make the drivetrain swap, however. If you are swapping the Cummins diesel engine, you may have trouble getting the engine mounts to fit the frame because the pad height is different. If two wheel drive, note that the half ton front suspension is not rated over 3300 pounds vs. the 4000 lb. front end used with the diesel. With four wheel drive, the Cummins uses heavier springs and bigger diameter spring eye bolts to the frame brackets.