Might look into the M139 set up from the original 5 ton series. As you likely know, the first 5 ton versions ran a couple of tire sizes; single 14:00 for the narrow bed cargo, and then dual 11:00 for the rest of the initial line. The slightly later M139 was the wider, heavy carrier (boat launcher, prime mover) and it carried dual 14:00 tires with front and rear spacers to provide room for the full width of the double tires in rear and to clear the fender well structure in the front. The spacers have turned up on the site and I got some from TNJ Murray in the past. Longer studs and the early 5 ton wheels should then get you able to use your new tires as duals. All these wheels were stud piloted; width shouldn't be a problem with the increase to 8 1/2 feet allowed across the board, and the 12 size would give you a little top end speed increase over your originals.
I've been running the last series 5 ton tires and wheels (14's) as super singles on my M916A1 with great success, but to support the full load carrying capacity of the truck, the dual 12 set up would be better.
John
