OK....Many thanks to TrailReady that loaned out this mockup wheel so I could really dial in the backspacing. It’s cracked clean through from racing KOH but it did the trick
Definitely assisted with finding the right backspacing. But.... unfortunately it's going to require some serious changes to our original plan. We were planning on running the factory Dana Dually hubs to match the Dana 70HD but it won't work. For those that aren't super familiar with M715's, they are VERY wide from the factory so it's hard to match the factory axle width with an axle swap.
So, we're ditching the D60 dually hubs altogether and going with SRW hubs and wheels with 3.5" of backspacing. It'll allow full steering lock to lock and with 2" of suspension lift, essentially no sheet metal trimming to run the 40's. As an added benefit, this thing might actually fit down some NW wheeling trails.
Wheels are on order so I moved on to trimming the rear frame down. In total, shortened it 22.25" as I wanted the truck to have extremely good breakover angles
I do not love cutting frames but if you're going to do it, do it right and take your time