You'll need more than the TJ header to use a TJ top on your YJ. Im most of the way through a YJ to TJ top conversion right now. My 90 had a sport bar, so I am also converting to a family style bar (the TJ standard roll bar) AND using a frameless Bestop Trektop NX- which seems to have added even more complications.
One big obstacle you will find is adapting the TJ door surrounds, because YJ spreader bars are not the same distance apart that TJ bars are. The door surrounds are a big part of my reason to swap to a TJ top, and are required to use every TJ top I have seen.
Check my thread, and you can see what Ive been doing for the swap so far.