Budnik wheel backspace

[ShinyC10]

Wondering if anyone can shed some light on what they have run on their wheels backspacing, front and back. Ideally, I would like to have some sort of turn radius when aired out or a couple inches higher than completely aired out, if possible. I plan on having a bump step welding up to stop be a few inches from completely bottomed out. The back I’m just looking for the wheels to tuck as high as they can. Was looking at 20x8.5 and 20x10 budnik spyders. Tires, I was looking at 235/40/20 and 285/35/20. Thanks in advance

1986 c10 pickup
Front:
Factory control arms
Vannatta front inner fenders
Bags with plates and cups

Rear:
Stock bed floor, tubs and rear end width
Ridetech bolt in 4link with the shockwaves