The swap is done! And it works beautifully. Thanks for all the help, guys. Will check for leaks tomorrow. And..
(Cross posting from another forum)
I believe I have fixed my NP242 'bucking/banging' problem in 4x4. As I've said before, when in 4x4 and especially full-time, I would get a BANG now and then and one time it got so bad that I heard a BANG and then nothing but grinding sounds. I knew it wasn't popping out of gear because the lever never moved, and the 4x4 light's never changed or went out.
The problem? My front vacuum disconnect. During the time I swapped the NP242 in, I moved the shift fork over with washers and nuts to permenently engage the two-piece axle shaft. I suppose it was either grabbing or shifting enough under different torque loads to cause it to free up and case the bang and grinding sounds.
I spent the last few days tearing apart my front end and replacing the whole two-piece design with a simple one-piece shaft from the junkyard (off an '89 with an NP242 no less) and took it for a spin today. The results? Beautiful, beautiful full-time 4x4 with no more horrible banging sounds underneath. I drove for an hour and not ONCE did I get any odd noises. I took it up multiple hills, revved the crap out of it, cruised, etc, and couldn't get it to bang once. Problem hopefully solved!
TLDR: Front vacuum disconnect must have been screwing up. Replaced with single-piece shaft and all is well!
Winter is fun again!