I just put some 15x10 with 5.25" BS on my '72 with the wider rear end. I have also removed the inner fender which let me run so low with only 1/2" between tire and fender. Your backspace will be more critical the lower you go. If you're tucking tire then you have to pretty much nail the BS because squeezing a tire that wide between the inner and outer fender doesn't leave you much clearance.
