unfortunately it is way easier, better, and cost efficient to sell the 4 banger. it is just as much work to swap a 4.0 in a 4 banger jeep as it is a 350 or any other engine. no one wants to hear sell your jeep, because we become attached to the jeep we have, i know i am. after owning both 4 banger jeeps and 4.0 jeeps, i'll never buy a 4 banger again.
having said all that, after getting all the parts for a donor, engine, trans, t case, accessories, computer, wiring and all, the other big problem is the motor mounts are different. the 4.0 motor mounts are further forward than the 4 banger, so some fabrication required.