Welcome to the board! I'm not an expert with the NP/NVG transfer cases, but unless someone else here chimes in, I'd contact the folks at
www.advanceadapters.com about what's required for the swap.
I've been inside the NVG-263 used in the GM HD's, but I'd recommend seeking local help if you're a first timer. The input shaft/spline shouldn't be a big deal to change - assuming the right one is available.
Also, I met the guy behind
www.fordcummins.com. He knows quite a lot about the conversions involving the Superduty and the Cummins.
Jim