8" wheel with 4.5" back-spacing works great on Plymouth b-bodies. Be careful as Dodge (Super Bees for sure) have a slightly larger wheel well. I can run 275-60-15 tires with no rubbing issues at all. I have photos, but can't seem to post them. I can fit an entire finger between the back of the tire and the leaf spring, as well as on the outter lip of the fender. This is for a '69 Road Runner. I'm guessing the '70 is similar, if not exact.

As an fyi...lots of the stock eliminator guys and fast street racers go with a 15 x 10 x 5.5" back-spacing. They use the same tires. It gives a different contact patch, and an entirely different look.