Duster 275/60/15

I have 71 Duster with stock A body 8.75 rear end with small bolt pattern and springs in stock location. I am looking at getting 15x8 rallye wheels form wheel vintiques and putting 275/60r15 on them. The wheels only come in 4.625 back spacing though. They do custom back spacing at a price though $50 a rim. I have made the measurements and done the math it looks like 4.5 would be ideal back spacing. These are so close, just 1/8 inch more back spacing. The math says they will fit but will be close. Was wondering if anyone has real experience running the 275 tires with 4.625 back spacing?