K2500 Tranny Swap

I own a 1990 Chevy K2500 4x4 (8 lug) with a cast iron 4 speed (L-1-2-3), NP208, 14 bolt rear, and V-8 350.  I am interested in swapping the 4 speed out and replacing it with a TH350 or TH400. I understand none of the 88-98 3/4 tons came with the TH350, but am told it should "bolt right up". I see many TH350's have different overall lenghts and am confused on the correct length I would need. I think (?) the TH400 will bolt up and have a common length in 4x4 applications as some '90's came with it. I am not interested in the 700R4, eventhough many builders can cure the problems normally associated with their common failures. I'm assuming I will only need the tranny, torgue converter, flexplate, aftermarket floor mounted cable operated shifter, and aftermarket cooler? Any information would be appreciated, especially on the tranny  requirements. The motor is stock, so I'm not concerned about the TH350 longevity. Thanks.     

you may have to change the tail shaft on your th350 or th400. I would go w/ the th400 , it will hold up a little better.  

Everyone I've spoken to agrees with your TH400 recommendation. Thanks for the input.  

I had an 84 Suburban with a L-1-2-3 trans, 350 and NP 208 case. We swapped to a TH400 with no adapters... the trans crossmember was moved rearward and the rear driveshaft had to be shortened. Good luck.  

90 might be a 241. That was about the time of the change over. It will be a 32 spline. Those years are the round bolt pattern You need to find a 82 or newer TH400 for it to work.  Snoop arouind www.ck5.com Those show up from time to time. Also www.pirate4x4.com Just watch your mouth and don't post till you know what's going on. Other wise you might join the band.  I may have exactly what you need for sale in a few weeks. Might be parting a 85 M1008 (military K30) it has a low mile 400 and 208. It might be under 30k. It will end up posted at both those sites. It could also be aranged to get the Auto peddle arangment AND the kick down swith and harness. The 208 might also be available. There is another guy here that you could sell your transfer case too. he could run the case you have.

 If your truck had come with a TH400 it would have been wired into the ECM. It would down shift it depending on load on engine. Your going to have to old school with just the passing gear.