275/50/15 Nitto NT555R no tubs or rubs

anyone running these on a Dr Diff disk brake stock width 8 3/4 housing. I just got my Dr Diff rear disk setup in along with the inboard leaf spring kit, and it looks like I'm going to need a 15x8 wheel with 5 inch backspacing to make it fit in the very center of the wheel well.
4.5 puts it way too far out and into the fender lip, and if 5 inch is a tad too much, I can always run a thin spacer to move it out a touch. My measurements puts the tire at least 9/16ths away from the leaf spring, which should be enough.

Just ordered the wheels from Wheels Vintique, now the waiting part. Tires are 275/50-15 Nittos.
Here's the setup ready for wheels.