1974 Duster wheels & tire size

They are correct, not all cars had lbp. I've seen quite a few with sbp but all were plain Jane six bangers.
I'm running 15x8 on rear with 4 1\4 backspace, 255\60-15. The front are the original 14x5.5 with 215\70-14. The rear is fine with enough clearance that I've never had a problem after 23 years now. They are tucked up into the wheelwell nice.