Looking at a package deal for a set of wheels. I have a stock '66 with a fresh Kelsey-Hayes disc brake install. The 15" X 7" rims in the package have 3.75" of backspace and an negative offset of 6mm. I've seen on charts the correct backspace is 4 inches. Will these be ok with 205/60R15 tires? Anyone have experience with this size on this year Mustang?