After destroying another NV3500 transmission I decided I needed to upgrade (again!). I didn't want to loose my overdrive so I went with a NV4500 from a 94 Chevy 3/4 ton. Now I had to find a transfer case to fit. I could have bought a NP241 to bolt straight up but then I realized I had a NP203 and NP205 stashed away from previous scrap vehicles. And as luck would have it the 203 already had a 32 spline input to match the NV4500 and the 205 was from a 78 Bronco so it had the driver's side drop that I needed. After pulling the 203 range box from the rest of the case I began measuring bolt circles and pilot diameters for the two cases. After gathering all the needed info from the 2 cases I used AutoCAD to draw up a 3 piece adapter that could be welded together. Once I had the adapter drawn one of the machinists at work programmed the CNC mill and one Saturday morning we made the adapter plates. Special thanks to Jim Jordan and Junior Burlile for all their help! Thanks to Travis Dunhoff for tig welding the adapter together for me. 
While I was waiting to make the adapter itself I removed the output shaft from the 203 and sent it along with a print to Moser Engineering to have it shortened and resplined. The service was excellent. I sent the shaft on a Tuesday and had it back that Friday. Below is the 203 with the factory shaft follwed by the 203 with the shortened and resplined shaft. 
The 203 range box with the adapter installed. 
Now that most of the parts were gathered I removed the old tranny and installed the NV4500. It was a tight fit even with the 1" body lift but everything clears. I attached the 203 and made a new crossmember to clear the larger tranny.  Next I made the modifications to the 205. First thing I did was remove the shift rail and enlarge the detent notches for true twin stick capabilities. The hard part was coming up with a vehicle speed sensor on the old 78 case. I used the 205 speedo cable to make a plug for the current hole. I milled a new flat and tapped a hole for the new speed sensor from a NP241 so there was approx. .040" gap between the reluctor ring and the end of the speed sensor. The hole was also located on the shaft center rather than offest like the speedo cable. Special thanks to Ken Steidle for helping me with this and for water jet cutting the profile on the adapter plate! I pulled a reluctor ring from a parts NP241 and it had the same spline as the original speedo gear. However it was about .125" too wide so I ground .063" off each side. 
The shifters were the toughest pieces to fabricate. With so little room between the tranny and floor boards, I couldn't just have the lever coming straight off the pivot. I had to make two brackets for the pivots to bolt to the tranny then have 90° plates extend up and over the tranny to where the rod used for the lever could be welded. I also added grease fittings to help prevent wear. 
Now I needed some matching shift knobs and some shifter boots. I called up the guys at WFO customs and ordered their twin stick 205 knobs and their 203 range box knob along with a dual stick shift boot and a single stick boot. I used the factory S10 transmission lever and made an adapter to mate it to the NV4500. The factory S10 4x4 shift boot was cut out so that the new double boot would fit tight inside it. The single boot was mounted just to the right of the original console for the 203 shift lever. I just need to replace the 22 year old factory floor mat that is ripping next to the console. 
I was now able to start the final assembly and finish making the shift linkages and the added crossmembers. The shift linkages were made from 3/8" rod ends. I used one left hand thread and one right hand thread so that they would be adjustable without having to remove them from the truck. A crossmember with a transmission mount was made to be attached to the adapter plate right behind the 203. 
The crossmember that already connected the two rock rails together was moved rearward to make room for the 205 and a mount was made that went to the side of the 205 to prevent it from trying to rotate. All the mounts and crossmembers probably seem like overkill but I wanted to make sure the added torque from the doubler was not going break the adapter. After getting a set of driveshafts with the 1330 double cardan joints cut to length the truck was ready to go. 
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