Have you thought about the NV4500 with a transfer case attached, like from a Dodge PU?
There is no such thing as an overdrive to go on the side of a transmission or on the PTO opening. It will have to be either before or after the transmission, and in line with the center of the input/output.
If you could attach the OD unit to the back of the NAPCO transfer case that may be an option. But I doubt they have a kit to do that. Is it a regular transfer case as used in other applications, or only NAPCO?
Many of the newer 2wd transmissions are quite long with the 2wd tail housings, this makes them more difficult to fit between the engine and your existing transfer case.
You can get some pretty short shafts, but 6" may be pushing it. Yhe need for aslip joint is part of the problem, as you need enough spline engagement to take the torque, that takes a little bit of length to make it work. I agree that you must have a slip joint there.
You can call a driveshaft shop, like
http://www.4xshaft.com/index.html and ask what they can do.
Grigg
