Differential Identification:

All GM 8.875 in.12-bolts use C-clip–style axles and covers attach with 12 bolts. The passenger car 12-bolt has an oval-shaped differential cover, and it measures 10 15/16 in. x 10 5/8 in. . The Truck Version has an irregular shapped cover with a ring gear pocket from top to bottom. Most passenger car 12-bolts used a four-bar trailing arm mounting system, with the exception of the Camaro and Nova, which used leaf springs. GM trucks from 1965 through 1967 used a two-bar trailing arm mount, while the 1968-up trucks used leaf springs.There is some crossover on the trucks, as some earlier trucks had leaves and some later trucks had the trailing arms.