what size tire and backspacing

In the rear: 245/60/15 15x7 with 4.25 backspacing or 255/60/15 15x8 with 4.5" backspacing. Might need very slim spacer. 4.25 backspacing might be better but not very common with 15x8 rims.

IRRC, Yukon axles move the flange out about 1/8"-1/4" outward