When I did my swap at first I got the engine harness and ecu only.
It didn't work for 2 reasons.
1) The body harness to the fuse box contains a million fuses for various engine controlling modules. To adapt your current fuse box to work with the new engine harness was harder than making the new fuse box adapt to the your old body harness. I.e: Using the new fusebox from the 2jz donor and wiring in your old radio, turn signals, ...etc into that. Instead of trying to wire your new harness into your old fuse box.
2)The body harness from the donor car creates a circuit that you'll leave open if you don't bypass it, or wire in the donor-car body harness. You can do what I did, and go through every single pin on the ecu, figure out if you need it or not and close/loop it. but it's a huge job.
This is assuming that you aren't getting a custom/pre-made harness and plan to do the work yourself. The whole donor-car wiring diagram will be your bible. http://www.shoarmateam.nl/upload/MKIVSupra/2JZ-GTE%20ECU.jpg