Did a transfer case service today along with a skid plate. Not all WJs came stock with the transfer case, but if you find a stock one, it mounts right up. I did have to modify it a little due to my lift kit. My existing lift kit has a transfer case crossmember drop on it of about an inch, so the skid plate wouldn't reach the frame without matching that.
The OEM flag nuts that would be inside the frame are expensive and only come from the dealer. On my rig, being that the factory flag nuts weren't present in the frame, I tack welded some nuts on the frame and bought some spacers at ACE. I just made sure the spacers would go around the nuts and welded them to the skid plate I got used off of eBay.
Painted everything up and mounted it on. Took about an hour for everything. The skid plate bottom is the exact height as the crossmember so I didn't really lose any ground clearance and now the tcase is more protected.