it must be a Ben thing, I just chased out something very similar on mine. Turned out to be the bushing between the intermediate and exterior axle shafts inside the 4WD engage housing on the passenger side. If its a noise that sounds like someone put gravel in your diff, I'd take the shift motor off of the axle tube; you will see where a shift collar moves over the split axle. If this joint has any slop in it, that's your problem. Remove axles and replace pilot bushing. I couldn't find one, so I machined a bronze replacement. But yes, I believe it was 1-11/16". I would NOT remove the castle nut while its still on the ground. I blew a wheel bearing doing that. The compression between the nut and the inner race flags is what provides all of the bearings strength.
Hope that helps.
KCCO and Keep it Dirty
'94 Ram 1500 5.9 4x4
'15 Challenger R/T 5.7... not 4x4