That's interesting. I wonder if you lost some space by having those parts off of the car? Like, maybe they're stretched a bit when welded into the chassis.
I know that AJ/FormS had his fastback measured at 13.25" from inner wheel tub to outer, below that bump in the outer so you'd lose room there still. But your measurements would put the absolute max at about 12.5".
Maybe the fastback and notch's really are different in the wheel tubs...
