8.75 : The build sheet would tell for sure. I would have to look up to see if the rear axle was on the fender tag. The early 65's came with 7 1/4" rears and the A861 Power Pack option would damage them. If it was a late built car it could have left the factory with it or was replaced at the dealer. That is what I remember reading which could be wrong info. @65dartcharger would know for sure.