If you have the same wheels with the same offset as others are running with the same tires, and you have that much interference then its pretty simple.... someone changed the differential at some time in the car's life and replaced it with one that was several inches wider. Only way to tell for sure it to measure drum to drum width.

Centerline
64 Dodge Polara 426 Street Wedge - For when I want to go fast
99 Corvette Z-06 - For when I want to turn corners