Fitting the TJ to the YJ is far more common since they're (apparently) easier to fold than the YJ tops. You should be able to find a thread on this, and you'd know what was modified to make it fit.
Off the top, I remember you need a header bar for the windshield, and swap to a TJ roll bar as the YJ bars are too big. Redrill for the TJ sill plates too.
'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4½" & shackles, BFG 33's (sold)