17" TorqLites on a 73 Duster

So... is 4" back spacing "ideal"? What about up front?

Ideal for the 275-50-17's. It depends on the shape of the tire, specifically it's max width and it's tread width. My measurements show that for my car, with the 8.25" rear, a 4" BS would mount the most tires in the center of the wheel well, which has a max width between leaf springs and inside of fender lip of 11 5/8". Below is my amatuerish attaempt at measuring the wheelwell opening.

Up front, the 4" BS is fine.

ScreenHunter_14 Feb. 07 22.15.jpg