15X7 w/4in BS Tire Size Question

Are you running small bolt pattern original axles? Including original axle re-drilled for LBP?

OR aftermarket or shortened large bolt pattern axles?

With small bolt original axles, I've run 4.25" backspace rallyes with 245/60/15 on my 68 Dart. Close on inside and outside with a very low leaf spring worn out rear end.

LBP aftermarket/shortened axles move the axle flange out 1/4" or so. Then you will need 4.5 backspacing.