Does anyone know if the NSG 370 (6 spd trans) will hold up behind a GM 6.0 litre or a 5.7 Hemi or 6.1 Hemi? Does Novac or Advance Adapters or anyone else make a kit for that swap. I have done several swaps on older Wranglers and CJs but now I want to build an LJ. Any help is appreciated.  

Nope, sorry. The NSG is not up for that kind of power. It's a great light duty transmission but a V-8 is a little much for it. You'll need to swap the tranny as well. An NV4500 or even an NV3550 can be used.  

Thanks for the advise. Now I need to find a wrecked doner 1 ton. It will probably be cheaper that way.  

you dont need to find a 1 ton doner to find a nv4500...look for what GM calls the "W/T 1500",the pup has w/t1500 on the tailgate and both doors, and in the glove box look for the code MT8 or MW3....my 93 k1500 is the W/T 1500 model and came w/nv4500 w/6.34-3.04-1.67-1-.75 and rev of 5.61 and i believe it was from 92-94 had the option tranny and was the strongest of the other yrs.
i have over 160K miles on my pup and not one problen to tranny other  than replacing the clutch.  

ive had some people in other forums argue w/me about my tranny saying that gm never put an nv4500 in a 1/2 ton pup but they were wrong and gm did put the nv4500 in only a handfull of 1/2 4x4s for work "W/T 1500" mine has the 4.3 v6 too and the combo is pretty good and stout,not much for speed though but its tougher than anything ive come across.  

Another good swap for the LJ/TJ is the Dodge 318 or 360. You can find 'em in Dakotas and Ram 1500's mated to 3500 manual trannies (same as 3550). This is an easy swap.