You will need just about all the electrics from the donor. Including the ECM and all sensors. Including exhaust sensors. Fuel system etc. If you can fabricate, read a wiring schematic and mark all wires as they are in the original vehicle. You have won most of the battle.
The truck won't know the extra weight is in there. May even ride better..Good luck.
A friend of mine did the same swap on an old Studebaker.. Loves it..