I also had the same size tire and backspace with a 10" rim and no rubbing (but close to outside lip) and lots of room to move the rim closer inside the wheel well. a 5" backspace would give lots of room all around, especially if she is lowered. I am not sure how 1970SS385 had the tire rubbing on the inside with the backspace he mentions. Must be a typo as the tire would be sticking out the wheel well, and rubbing on the outer lip, with lots of empty room on the inside..
1973 RS Z28: 401ci Dart Little M, Littlefield 8-71 supercharger @14lbs boost, Callies Magnum crankshaft, Lunati Pro-Mod rods, JE pistons, 7.8:1 compression, AFR 227 Comp heads, T&D 1.6 shaft rockers. Reed solid FT cam (240/250@.050, .523/.542 lift, 112 LSA), QFT 750 carbs, Lemons headers, Mezier mechanical water pump, Tremec TKO-500 5-speed, Moser 12 bolt, 33 spline axles & 3.42 gears.