JCI 1038 front diff gearbox- different from TC3?
 

everything in the title (to save people's time:))

If it is the same, I don't undertsand why it has a JC part number (same thing for the rear wishbones which I thought came from B4)

They are different.

Here's a pic for starters: -

http://www.losipartshouse.com/catalog/ASC2368-450.jpg

That saves a bit of typing.

Also the front is angled, the same as the kickup on the BJ4 to fit in the front bulkhead.

Hope that all makes sense.

The transmission housings are TC3/TC4 housings, but the bottom halves have been modified (both front and rear). The legs are shorter (plus angled in the front), and some extra material around the input shaft has been removed.

Similar story with the B4 rear arms. Material has been removed for extra clearance, and a hole has been added for a sway-bar mount. However, the B44 rear arms have the sway-bar mount molded into the arm.

In a pinch, both modifications can be done with a Dremel and a steady hand.