Some of the 91 N/A's came with a smaller rotor. It could have a 9.375 rotor or the 10.25 rotor. The 10.25 rotor is the same rotor used on the XR2s. The knuckles made for the smaller rotor will not work with the larger rotor, the caliper bottoms out before it reaches the mounting ears on the knuckle. Does your N/A use the larger XR2 rotor?