Re: TH350 or Th400 ??? in my CJ-7
This is just my opinion, but...
The TH-350 will probably live doing almost anything you can put a jeep through.
The TH-400 really isn't necessary unless you are making more than 400 to 450 honest to god horse power, and able to apply it to the ground.
(Applying 400 HP to the ground is no small feat! Ask any drag racer.)
You may consider the TH-700R-4 also. It is much stronger than the TH-350, and almost as strong as the TH-400, but lighter, gives you an extra gear to keep you in the power band, can be used with or without lockup converter, doesn't waste power like the TH-400, and is something that not every off-roader has.
I saw the adaptors and tail shaft kits for under $200 in two different off road catalogs recently.
Good luck and happy trails.