I think OE used 3.5" BS for the 6" wide rims, and maybe as much as 4"BS for the 7" wide rims. This was with the factory skinnys (215 wide maybe?).

I ran an 8" wide 4.33 BS on the front for a while, and it put the 235 tire even with the fender so had to go down to 225. With a 7" wide rim, it might've been about perfect I think. Too much BS and you can add a shim or bolt-on spacer if you have to. Too little BS and tough luck.