I’ve run 15x7 cop rims that have the same as stock 15x7 rallyes: 4 1/4 backspacing.

That clearance is the same as a any E or B body with the only exception of the upper control arm. Is your UCA original or repro? Are you rallyes OE 15x7 or repro?

Also notice this is with the suspension all dropped down. Do you have the UCA bump stops installed? Even with them it’s close. When you put it and ride height, that clearance gets bigger.

If you haven’t aligned it yet, you could have too much negative camber (top tilted inwards). And would reduce that clearance.

I’ve run 15x8 rallyes with 4 1/2 backspacing. That’s a 1/4” closer. I had a tire blowout and it knocked all the inside wheel weights off.