Just an FYI, if it is an "Olds" 12 bolt, it is not equivalent to a Chevrolet 12 bolt. Oldsmobile 12 bolts from the early 70's had 12 bolts in the cover but did not have an 8.875" ring gear like the chevy 12 bolts did. Oldsmobile 12 bolts utilized an 8.5 ring gear. It's basically a 10 bolt with a 12 bolt cover.