15" Rear tire sizes for Duster

I have a 72 Duster with an 8.75 rearend and stock suspension. I talked to a guy on another site that said he runs a 15x8 wheel with 3.5" backspacing and a 275/60/15 tire so I bought the wheels in that size with a 4.5 bolt circle. Now I'm wondering if I should have bought the 4.5" backspacing wheels after reading a couple threads on this site.

My stock steel wheels had 3.5" backspacing a 245/60/14 tires, it seemed like they were pretty darn close to the leaf springs so I was afraid to get a 4.5 backspacing wheel with a bigger tire like the 275/60/15.