if this is for a chevelle or a-body, the only 8.5" rear that would fit was in a 71-72 olds cutlass or buick skylark. chevelles didnt get 8.5" till 73 and wont fit the 64-72 a-bodys , the really good thing about the cutlass/skylark rear is they have bolt in 28 spline axels =no c- clips are needed
novas got the 8.5" in 72 camaro/firebirds got 8.5 in 1971 but ONLY the a-body 8.5" had bolt in axles - rest are c-clip type