The truck 12 bolts are different from car ones. You would have to change the side gears in the posi unit if the splines were different...I have never had any luck trying to piece something together. A used posi unit at a swap meet should be around $200 . Make sure you get the right one though as there are many 12 bolts out there : Chevy car, Chevy truck, Oldsmobile, and variations thereof including 2, 3, and 4 series carriers.
Dave
