Looking at buying a Square with Dodge guts...

[playinsafe44]

I'm talking with a guy regarding his square body chevy that has a 6BT in it that he wants to sell. Right now I'm very interested, but I don't know a lot about the cummins engines. He says the 6BT was swapped into the truck in 1990 (1st gen?) and only has 90,000 on the engine. It has a TH400 and he says it has a NP203. There are a few things I'm not sure about.

1. The intake crossover pipe looks different. Is this a industrial application?
2. It still has vacuum brakes. I thought there wasn't enough vacuum to run these, and that's why everyone goes with the hydroboost swap.
3. He claims it's an NP203 (fulltime 4WD), but he said the shift pattern is 4H.4L.N.2H.2L. He also says he has new milemarker hubs for it. Is this an NP205?
4. This is not an intercooled engine. Can it still be upgraded like the rest of the 6BT engines? I think I would want to bump the power for towing, and try any mods for increased MPG.

The price seems reasonable, but I don't want to buy a lemon without knowing what to look for.