I'm running the 5 lug disc conversion with 235/70/15's on 7" rim width and 4" back spacing on my straight axle 54-3100. With the stock tie rod ends I had about 7/8" clearance. With the upgraded tie rods I have additional clearance.
I run 255/70/15's on the rear with a 62" Camaro diff (same as stock width)and run 15 X 8's. I tried the 8" rims on the front with 235's and still had plenty of clearance from the tie rod ends.
If I had to do it over again I would run 15 X 7's with 235/70/15's all the way around...then I could do a conventional rotation.
I think you would be safe with 4" or even 3.75" as I don't have any clearance issues on the outside with the fenders and that would give me a tad more tire-to-box wall clearance on the rear. I also run front and rear swaybars.
Dave
