8.25 rear backspace for 15x10 wheels?

The 8.25 is a little narrower than an A-body 8 3/4 with BBP axles. For a 10” wide rim with an 8.25 you’d want a backspace of about 5.25” to maximize the rear tire size with the offset springs.

As for the quarter lip, it depends on how big of a tire you want to run. You can fit a 275/60/15 in there without cutting anything. Biggest tire you’ll actually fit inside the stock wheel well is a 295, and to do that you’ll probably have to trim the quarter lip all the back to the spot welds between the quarter and the outer wheel well. But that will depend on your car specifically, they’re all a little different and if you max everything out the body tolerances from one car to another make a difference. Same with the backspace, that should be close but always measure your own car before you start ordering parts.