Given you're in Cali, I'm guessing to swap to the 4.0 you need to take all the emissions control stuff with you for CARB compliance?
The evap pressure sensor I believe is a separate unit on the vapor line. I Googled images of the fuel tank and sending unit and it's not there. I then did the same with "96 cherokee vapor pressure sensor" and it's showing a stand-alone piece. BTW, this thread is the #1 response to that query.
If it's a separate piece you should be able to Tee it into the vapor line.
'91 Frankenheep YJ. 4.0, 4" BDS, Richmond 8.8, Titan 12k, 35" KM2's, rust.
'88 YJ, 4.2/4.0 head, +4˝" & shackles, BFG 33's (sold)