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.
The only car that had an axle as wide as an E body was a C body. The C body cars never got a 7.25 axle as far as I recall. What if the car has replacement quarter skins? Those sometimes have thicker wheel well lips than a stock quarter.
