OK, so all the credit (or infamy) goes to my brother
for this mod and we are not assuming any liability for latch fit and function in an accident but here is a quick and dirty way to put YJ lower half doors on a TJ. The hinges and physical size of the door are pretty much a match so it comes down to the latch mechanisms. Bear in mind, the uppers doors are different between YJ and TJ so I cannot say they could be manipulated to fitted.
Remove full doors (top optional)
Remove stock latch bar.
Buy a door striker kit from the nearest HELP section in your autoparts store. Add 7 washers...
assemble in the factory top whole and voila, a YJ striker post on your TJ.
Trim 1" off the inside door handle. Optional, if you want to open the YJ doors from the inside on a TJ due to interference with the dash.