If the '86 was originally a V8 model, it had an 8.8" rear as original equipment. If it wasn't originially a V8 it had a 7.5" rear. But that doesn't mean the rear is original.buddry said:How do you figure what size rear end is in a 1986 Mustang? I need 3:27. I don't know if it a 6.75, or 7.5, or 8.8.