71 and up (may go back to 67 or 68) "C" body, 74 and up "B" body, and 1/2 ton trucks all share the same axle housing for the same size rear end (8 1/4, 8 3/4, 9 1/4). Car spring pads are on the bottom of the housing because the housing sits above the leaf springs. Truck spring pads (except 1st gen 2wd Dakotas) have the spring pads above the housing because the axle is mounted under the springs.
73 and newer cars used a rubber encased axle to leaf spring pads that you would probably want to change over the the truck pads that mounted directly on the springs. Gene