I believe that none of the first generation Firebirds came with 12 bolts. That was a Chevy thing. (The 6 cylinder, and low HP V8's got the 10 bolts, the higher HP V8's got the 12 bolts.)Pontiac used their 8.2 " 10 bolts with all engine options.(from 1bbl OHC 6 to the Ram air 4 400)(Pontiac beefed up the rear axle with a heavier differential on the higher HP engines)If you see a First gen with a 12 bolt, it has been switched........