The T18 has a spacer on the front so that the shifter doesn't end up under the dash. The 80+ T18/NP208 is actually a very rare setup. And that version of the NP208 won't work behind many other transmissions. Its best to keep that T18/NP208 setup together. If you are going to sell them to another FSJ owner, they would need them together as the trans isn't of much use without the t-case.
However, finding a 23 spline input driver drop NP t-case should not be hard. Although as I recall there was two versions of the 23 spline input.
As for the swap itself, plenty of people has swapped in NV4500s. You will need to bend the shifter to clear the dash. But another question is, which NV4500 do you have? The gas V8 version or the V10/Diesel version? If you have the diesel version, I think you need to swap out the input shaft to work behind a gas V8. And you will need a bell housing adapter, and a bellhousing.
The T150 bell housing is what you will need, and then an adapter like this:
https://www.northwestfab.com/AMC-V8-Eng ... _3784.html
Most adapters are for GM versions of the NV4500, the one linked above is specific for a dodge V8 version.