The S-10 NV3500 will not work for your application. While they will bolt onto your engine, they use a 5 bolt round bolt pattern for the transfercase instead of 6, and the shifter is right at the very tail end of the transmission, putting it up through your floor right about where your center console sits.
You need an NV3500 from behind a 4.3L V6 or 5.0L V8 (and rarely, the 5.7L) from a 96+ K1500. Absolutely avoid any NV3500 with an external slave cylinder on them. Not only does the slave interfere with your front driveshaft unless you've got a bunch of lift, but they are also extremely weak, and break very frequently even with just light and normal use. They also use a very crappy shifter assembly which frequently falls out of gear.
In about 96 they switched to an internal slave transmission, which is what you want to find. I am not sure exactly when they switched it, but there are two versions of shift rails. One is a single rail, and the other has several rails. You want the version with a single rail on it. They are the strongest version of the NV3500 from 88-98. GM continued using the NV3500 until at least 05, possibly up until 07.5. These transmissions are the ultimate in strength, and came behind 4.8L V8 engines which make more horsepower and torque than a Vortec 5.7L. I have one from an 04 in my K5, and have had no mercy with it power shifting and dumping the clutch over and over on it while mud bogging at full throttle with my 6.2L turbocharged diesel engine offroad, with poor gearing and 37" boggers with lockers. No signs of failure at all, no unusual noises etc.
Swapping them in is not a difficult task. They bolt straight in place of your SM465, using the same transmission crossmember in the same position, using the same mount even. They all have a 32 spline 6 bolt round pattern so you can use an NP241 or NP208. NP205 would not be a good choice, as there is no place for the shifter bolt. The clutch is the same as your SM465, no need to change the flywheel, disc or pressure plate. You need to use the hydraulic throwout bearing, of course. The shifter on these trucks sits a few inches back of the SM465, requiring you to cut the floor back a bit, and patch it up at the top. If you want to use the stock shifter boot, you will need to move the NP208/241 shifter back a few inches and shorten the shift linkage under the truck to match. To match the hydro clutch, I personally retrofitted a 93 K3500 bolt on type master cylinder onto my truck. I drilled a hole through the clutch pedal and used a 1/2" bolt with the head cut off / hole drilled through for a hitch pin to attach the linkage to the pedal. I have heard rumours, but have not tested just yet (give me two weeks...) that you can simply splice an 85-91 stock master cylinder to the clutch hose for the internal slave and use it without any trouble. Try at your own risk, you have to buy the master and the slave to get a new hose from GM. The reverse light wiring is a plug in kind of a deal, same connector as your SM465.
Let me know if you have any other questions or run into trouble!
