I did both an 8" and a 9". I knew the fixture wouldn't work with the 8" (well, it wouldn't bolt on -- it still worked fine for locating the brackets when clamped on) but I had the exact same experience as Blue Oval Man with the 9".do you have an 8" rearend? i noticed that Pete was working on an 8" on the mustang he did as well. if that's the case then that's also the problem, the studs on the 8" are in a different location than the 9". just an educated guess but i'd be willing to bet that's the problem.