I have, 265/50/15's Mastercraft G/Ts on 15x8 I think 4.5" B.S on my 64 Fairlane. Using 57 Fairlane 9" rear w/ drums. You will have to massage the inner lip that hangs down by the unibody rail to prevent the tires getting cut though. No issue after that.
With the right wheel you may be able to run a 265. Or drop down to a 255. Shouldn't be a issue.