71 Demon wheel size/backspacing

Guys, restoring my 71 Demon and I want aftermarket wheels. REally want a set of older slots.

The car is a 340 car with the original 8 3/4. Wondering what wheel width and backspacing I'll need to clear everything. I've found a 15" set of slots that are 8.5" wide. Backspacing is 3 3/8" on them. Will this clear? I've only seen slots at the most being 3 7/8" backspacing, will that work?

Also, plan on putting Good Year Polyglas on the slots. Wondering what size tire will/won't fit.

Thanks in advance !!