I've never worked with, or researched, a np205. I don't know much about how they vary from the np208 in fitment. post #6 of the following link indicates that sm465-fitted 85-91 np205 are interchangeable with the sm465-fitted np208 cases. Also, the np241 and np208 are identical in fitment. By correlation, the 85-91 np205 "should" fit in place of the np241 which came behind the nv4500 from the factory.
https://www.pirate4x4.com/threads/sm...-np205.519198/
It appears you have one of the rare desirable 32-spline np205 cases with the round six-bolt pattern.
A nv4500 is virtually the same length as a sm465, if both are 4wd. There are slight differences of less than 1/2 an inch, but as far as I know, that's just manufacturing discrepancies over the years. It's not enough to cause any issue with driveshafts.
A potential issue is the transfer case shift linkage. The nv4500 never had the connection point for the transfer case shift linkage that the np205 requires. You'll need to fab up a bracket, or buy one. It appears that Advance Adapters makes, or did make, a bracket for that purpose.
Edit to add: be sure to look over any nv4500 good before installing it. Ideally even before buying it. Remove the shift cover, the pto plates, and the rear extension housing. Look for any debris in the oil, check for excessive slop in the input shaft/mainshaft combo, make sure there are no chipped or badly worn gear teeth, and confirm that the fifth gear nut and gear are still in their correct locations. It's also possible to tell the general condition of the synchros, just by looking at the spacing between the sychro teeth and the engagement teeth. I'm not well versed on that, though. I bought a 1997 nv4500 sight-unseen, and intended to stab it in and run it as-is. I opened it up, and found that fifth gear was half-way backed off, the input shaft thrust bearing was gone, the 3/4 synchro hub was trashed because of that missing bearing, the parts of that bearing had chipped two gear teeth, and the synchros were heavily worn. I'm facing $1000 in parts to get this thing back in operable condition. If I had run it as-is, it most certainly would have failed in the first 100 miles. These nv4500's are not hard to work on, if you have access to bearing pullers, a press, and basic fabrication tools for making some of the specialty tools required.