Rims/ Wheels for an early A body

I’m in the process of removing my 7 1/4 rear. I’m going to be installing a 8 3/4 rear BBP. Stock wheel well openings. Wondering what is the largest tire rim combo I can install? I was looking at a set of 15x7 or would a set of 15x8 fit? The front wheels will stay 15x6.

TIA