69 valiant rear 1/4/tire and wheel measurement

I just put 15X8.5" on my 68 Dart. Tire is about a 10.1" section on tire 4-7/8" Backspace car sits low and it rubs just a little after I rolled the fender lips going around turns 15 X 8 with 4 1/2" backspacing would have been perfect. However Centerline doesn't offer that size