The NP231 and NP233 are nearly identical except for how they are actuated and the mounting options near the shift sector shaft. The NP231 is manually shifted while the NV233 is electronically shifted.

The NP233 can be made into a manually shifted transfer case with proper ingenuity. This typically requires a custom shift arm being welded onto the shift sector shaft on the transfer case (careful not to melt the shift sector shaft seal) or swap the shift sector shaft for one from an NP231.

You can browse the Classifieds section as well as post in the 'Wanted' section, but I don't recall any NV231 setups coming up in that section recently.

 

I swapped the manual NP231 into my '94 which came with the push-button NP233 and I haven't had any issues. Only reason I did was because I was having stupid issues with it at bad times. The final straw being when it got stuck in 4 Low. Also, when I bought the truck the previous owner included what appeared to be a fresh reman. NP231 so I just used what I had and made it work.

Early 1st gen trucks 100% came with manual t-cases, I believe they started offering push button 92ish and started phasing out the manual case from that point. I'd be surprised if they ever made a '96 with a manual t-case, I didn't even know it was an option in '95. It seems to me they're pretty rare after '94.

If you're looking for a nice ride for your girlfriend, I'd stay away from the '93-'95 stuff for her, as they are pre OBD II and when well-equipped have finicky electronics, mainly the ABS, push button 4x4, digital dash, and CPI fuel injection. At least once you get into OBD II (after '96) you can hook a scanner up to the thing. The '82-'91 trucks are about as simple as they could have been for the time, but she may not want to roll around in old stuff either.

 

I just saw a local ad for a 4dr--either was a 91 or 92, with 89,000 miles for $1995. Wish we had the cash to get it!