How to Measure for the correct back spacing?

I'm really proud of you. But the leaf spring isn't always the only obstacle. You ever use the Percy tool? Once you do, you'll wonder why the hell you did it any other way.

I understand that there are other obstacles. In the rear though the leaf spring is closer to the end of the axle then the inner wheel well. the only other obstacle in this case would be the inner lip of the quarter panel.