I am upgrading the 8" rear end on my '71 coupe to disc brakes. I know HOW to find the axle flange offset for the 8", but with the backing plate on the car I can't tell for sure if it's 2.5 or 2.66. I just got the drums back on the car recently and hope not to have to remove them yet again. Does anyone know off the top of their head what the answer is with 100% certainty? Or, is there anyone out there that has already made this upgrade to their 71-73 8" rear that can provide me with the correct Wilwood kit number?