d35 or 8.25 rear diffs?
Stuff you need to swap:
Transmission, transfer case, front driveshaft obviously, rear driveshaft, transfer case shifter linkages and brackets, front axle.
I'm not sure if the bulb is installed in the instrument cluster already, it should be. If it isn't, swap the instrument cluster, or stuff a bulb in it in the proper spot.
The transmission wiring will simply plug right in.
I believe the transfer case switch wiring goes as far as one of the connectors by the trans dipstick, but I'm not sure. When you pull the donor drivetrain out along with the harness, be nice to it, and look at how it plugs in. If it just plugs in, do that, if not, you may have to splice two wires to make it work, or swap the engine bay harness if you don't want to splice your harness.
I'd check my FSM but I misplaced the closest year I have to a 2000 (my 1998) and haven't been able to find it in something like a year now. Either way, it's two wires to the transfer case switch/sender, when they're connected together, the light comes on. Super simple, and since you have two of the same year for your swap, you can compare pretty easily.
The only remaining question I have is whether the recipient and donor have the same rear diff. If they do, you can just swap the rear driveshaft. If they don't, you need the rear driveshaft for a 1996-2001 4.0/auto/4x4 XJ with the same rearend as the recipient has. If the recipient has an 8.25 and the donor has a d35, find the right driveshaft, if the recipient has a d35 and the donor has an 8.25, do yourself a huge favor and swap the rearend and driveshaft, you'll want a new set of U-bolts to install the rearend, but it's worth it because the 8.25 is significantly stronger.