Swapping in a 4.0L for the 4 banger is just like any other engine swap, but you don't have to mess with any of the interior gauges.  The best way to do it is get a donor vehicle from the same or similar year and take the engine, tranny, t-case, computer, and underhood wiring harness.  The motors mount need to be cut off and new ones welded to the frame, driveshafts modified, new fan shroud, wiring, etc. 
I have done this swap and I used a 94 XJ as the donor.  The XJ t-cases are clocked lower so I had to modified my skid plate and the bulkhead connectors between the YJ firewall and XJ wiring harness was different so it was easily to wire in 2 more cylinders than trying to change the connectors