Ok, so I've determined the dodge axles won't work out.
I'd like to keep the rear spring hangers outboarded they way they are and not have to move the hangers underneath the frame. They problem is that I need a wider axle to fit the 50" width from spring center pin to center pin. The dodge is 50" between the backing plates so this has me headed to the CUCV route.

Also the auto is an A518 with .69 overdrive.

With 37" tires, 4.56 gears, .69 overdrive at 65 mph the cummins is at 1850 rpm.

With stocks M7## axles, 37" tires and .69 overdrive it's 2400 rpm, too much for the cummins. I'd like to be close to to stock which if my math is right is 32" tires, 3.55 gears, overdrive 65 mph is then 1670 rpms.