Just lay a steel ruler across the face of the hub where the back of wheel mounts. Then measure the distance from the ruler to your leaf spring. Deduct 1", and that is your max back space. My Dart measures 5.5" there, deduct 1", I get 4.5" max backspace. The tire will take up 1/2", then 1/2 " clearance to the leaf. That's how I understand back space.
