Well, I think you are headed in the right direction, except for your choice of engine and front axle. A rig like you describe, with appropriatly sized tires, is going to weigh over 5,000 pounds, so if you want front axle durability, you will need a Dana 60 in front.
While no one doubts the HP/Torque attributes of a diesel, but they make for a poor crawling motor. First off, the throttle response of just about any diesel sucks. They are just flat out not made for blipping the throttle, and that technique can get you out of trouble, or over a ledge-type obstacle very quickly. I used to be a fan of diesel rigs, but after running around the forest with a diesel pickup, I can tell you they are not the ideal offroad motor.
Second problem with that particular diesel is going to be packaging. When I looked into swapping a 3.9 cummins, the height of the motor was going to be a show stopper. As it is, my track bar kisses the oilpan on my 4.0, and the Cummins is like 5.5" taller. Combine this with the aforementioned Dana 60 front, and you'll have about 2 inches of uptravel.
Have you actually priced a Cummins motor? A 3.9 was going to cost me about $4,500. While the 5.9 are a little less, they are still fairly pricey, especially Cummins Repower units.
Your rear axle is likely a 30 spline unit, but it may have spindles large enough to accept a 35 spline axle. Dodge changes stuff all the time, so it's hard to know the width for sure. I would guess it's about 65 inches.
Good choice on the NV4500, I love mine.
CRASH