NV3500 vs 4500 difference

[hatzie]

The 3500 has a torque limit of around 250-300ft-lbs. It may or may not put up with heavy towing and it doesn't have the lower 1st gear to get her going.

The other thing to think about is whether the 1/2 ton tires, brakes, and suspension are up to the task. On a lighter 1/2 ton you could easily end up with the trailer attempting to drive the truck instead of the correct way round. Both of my last 3/4 ton trucks came from guys that were moving up to 1 ton duallys to pull their big new 5th wheel campers.

As far as swaps like this go it's pretty straightforward. My guess is it's around a day or two of fiddling to get it to fit and since this as a GMT400 that already has a manual transmission it's maybe $100 in parts... $200 far on the outside and that's with the smaller Canadian dollars.

I'd get the propshaft(s) off the donor and use a hybrid universals on the diffs... if it's needed.
Moving the crossmember back is pretty easy.
I bet the 4500 shift tower is still under the 3500 hole in the floor. GM generally put a pretty big hole in the floor.