[CC69Rat]

Yep - The Wheelrite will get you within a 1/8" Easily. It also comes with a little wire like thing that will simulate the tire size. Just figure out how large you want the tire to be (how much sidewall) and with the truck at ride height .. jack under the LCA, not the frame .. measure where the tire would be with a 30" overall diameter, 29, .. however you want it to look. Then section width of the tire, try it with the wheels turned all the way to the lock, check for frame clearances on the oposite direction, etc.

This tool will allow you to stuff as much tire under it as you can !!

Take your time. Wheels are expensive. Measure 10-15 times. Find a tire you like and check their website for specs. Overall dia, section width, etc.

Talk to Keith ( lolife99 ) on here .. he knows a LOT about backspacing and was very helpful to me when I got mine. .. We'll get you fixed up man.

It will be the best ~$40 you can spend to do it right the first time.
Good Luck.