Tell me what i am missing here...i have a 66 valiant too, and I measure the rear wheel-well opening at about 10.5".
So how come 8" wide rims are not more popular for that a-body. Looks like most people are running 6.5" wide rims like your self?
I’m sure cause they will rub...I have had 15x7 and I think 15x8 Cragars too but they are tight....having super stock springs helps I’m sure but everything else on the rear of the car is stock.