71 Demon 15 x 10 Backspace Question

I don't have the correct answer for you, the only Duster/demon I ever messed with was mini tubbed with springs under the frame.
So, I can only say what I would do... I would ALWAYS buy the wheel with the most backspace. If it rubs the springs, spacers fix that (billet only please). If you don't have enough backspace and it rubs the fender, how do you fix that?
Edit: I have fine-tuned tire location with spacers on three different cars. Custom made hub centric 3/8 spacers on a eleven second car, 1/2" billet I made for a nine second car, and 1 1/2" on a former eight second car that has been slowed down to ten ohs voluntarily. Sometimes wheels aren't offered in exactly what is necessary.