I'll disaggree.

My `87 2.6 has so many V6 Mitsu parts swapped into it, he's better off doing as origially planned.

He wants the V6 front diff, half shafts, brakes, rotors, and all the pre-existing frame-related mounting points for the V6. Stay with the body swap. Keep the frame.
he only "advantage" to just swapping engine is that he would keep the rear leafs, which in my opinion are better than coils offroad. But otherwise, you'll find trying to bring over the front driveline as well a difficult chore.
Transferring just the body will be a lot of work, as he needs to swap over the gauges and engine control computer, (and use the V6 brake master cyl!) but it's probably the best way to go.

All the wiring exiting the firewall on the driver's side is probably OK to keep, as it's headlights A/C etc. But the passenger side wiring bundle is mostly engine controls.