A while ago I tried digging through parts books to figure this question out
I think the only difference on the rear axle is the studs pressed into the axle are longer to accommodate the extra thickness of two rims
And I need to track down a set of these longer studs for one on my trucks

The front axle I’m not sure as my dually lost it’s special dually front bits long ago and is single wheel style on the front now.

But i also look forward to the definitive answers that hopefully will follow.
-s