Not to confuse you any more but i had a 76 lemans that had this same rearend from the factory 12 bolt cover 12 bolt ring gear. Measured 8 7/8 but a standard g.m. 12 bolt ring gear would not match up. All i found out is that gm had alot of odd and end parts they put in their cars in the 70's. If you are not drag racing throw it out and put a weak 10 bolt 8.5 under it.