Need math confirmation on wheel offset

[TitoJones]

Hey guys, I have a interesting wheel/tire combo to figure out.
Here's the specs on the car:
1967 Camaro
Front hub to hub width: 61"
rear hub to hub width: 63"
front rim size: 20x11
rear rim size: 20x13
So far I have front with a 20x11 with 4.5" of backspacing, and 20x13 with 6.5" of back spacing.
He wants the wheels and tires to stick out at least 2" on each side so we can add flares to the car.
The stock sheetmetal is 71" in front, and 72" in the rear.
This gives me 4.5" from the rear hub to the rear 1/4 panel, and 5" from the front hub to the front fender.
Can someone confrim this for me?
Tyler