When I was deciding on the wheel width/backspacing and tire combo, I thought about mini-tubbing the bed to fit a wider wheel/tire. I took a lot of measurements, and I think your combo would work if you modify the inner bed sides like you said. What size tire are you going to run? Mickey Thompson 29x15.00R15 Sportsman S/R radial? I think you've got enough room to do that. 12 inches (the overall width of an 11" wheel) minus 6 inches backspacing = 6 inches on the business side. That's the same on the outside as mine with a 10 inch wide rim (11 inches minus 5 inches backspacing = 6 inches on the front side.) Should work if you modify the wheel well. Keep in mind that if you were to use the MT tire, the section width of that tire is 15 inches on a 12 inch rim ,so it would likely be only a little narrower on an 11 inch rim (maybe 3/8 to 1/2 an inch at the most) and you'd have to ensure the tire sidewall will clear any body or suspension parts.