My new wheels won’t fit

Too much backspace has an easy cheap cure called spacers. That wheel does not appear to be hub-centric anyway, so if you have the correct nuts for it, spacers are no big deal. And then once mounted you can check the other clearances. For test fitting, I have even used washers.

But IMO for track work;IDK why you wouldn't move the springs and or narrow the rear as may be required. I'm pretty sure the Duster/Demon tubs are the same width as my Barracuda, which easily accepts 295/50-15s on 10s. Miles of room.Centered in there I can rip around turns as hard as I want.... as well.