I have 33s I think on my M37, I wouldn't dare going higher but maybe I can. God knows I don't need bigger anyway. I wanted to go Dana 60s to get 37s Humvee wheels, disc brakes and a highway friendly ratio. But the hell with it, it's a camping truck anyway, we'll just go slower.
the stock dodge axles should handle 35s easy enough maybe 37s, but anything bigger would need the D60, I do run a D44 with 40 boggers in another truck but its got some top grade axles in it.
The GM axles in a 506 are slightly stronger than a 60 or a 14 bolt, but also a good bit heavier, About 400 lbs for the set!
I have a friend that runs a D60 center with Gm military outside hubs, it's a custom built rear steer piece, the axles shafts are special order and cost around $3400 for the set, they claim to be unbreakable , we shall see!