What's the best way to measure for tire size.

I came up with: Driver side, 6-11/16 from face to leaf spring, 4-3/4 from face to fender. Passenger side, 6-5/8 face to leaf, 5 from face to fender.

I'm putting 18x9 Bullitt wheels on the rear, I think the 265/35/18 will fit. The fenders are untouched stock, i have no problem w with modifying the wheel well.

What year Mustang had the right back space?