72 Demon mini tubed
Ok, so by that I assume it's still the 5x4" pattern too?
I run 295/35/18's on my Duster on 18x10's. It has a 1/2" spring offset but doesn't have the full 3" relocation or mini-tub. I have a 68-70 B body 8 3/4 in it, but that's easy enough to do math for since we know how wide that and the A-body 8 3/4 are. I've done a bunch of other stuff to my car, but for the purposes of fitting 295's with stock brakes on a Demon most of that is irrelevant.
Anyway, you'd want 15x10's with at least 5.5" of backspace, or 0 offset. As others have pointed out you can run a much larger tire on a Demon with a full 3" relocation and mini-tub, up to at least 335. And more backspace would be necessary for that. But for 295's on a 15x10 with the SBP a 5.5" backspace should be fine, and anything up to about 7" would work. If you have converted to BBP then I'd be looking more at 6" to 7.5" of backspace.
Stock A body rear with mini tub takes a 7.5" backspace on a 10" wheel iirc
Tha is the wheel specifications I am putting on my 64 Barracuda.
And for a Dart or a Barracuda that would be necessary, especially with a BBP conversion. For a Demon/Duster/Dart Sport there's at least an additional 1" of room to the quarter compared to a Dart. And then there's the extra offset from the BBP axles. Basically you're just adding 3" of backspace for the relocation from the 4.5" or so of backspace needed on a 15x8" if you're using BBP axles. But for a 295 on a Demon you don't need to add that much. You can, although with a SBP 8 3/4 I'd probably stop at around 7".