You can find a wire routing and replacing proceedure in the oem shop manual. Its a lot of work. I would do a connector count and see if they are the same color and fit. If so you may be able to run any wires you need. But if some of the wires are crossed in the factory harness will trip you up. Replacing the entire harness is the way to go. But will require careful planning and lots of tome making sure every thing goes right where the factory says it needs to go. Try not to cut and peice it back together it never last and always causes problems. I would really try to avoid unwrapping or modifing the harnes as little as possible.
Dont forget the trans harness and computer if its seperate for the ecu. If they are intergrated and the trans are different. It could be wired differently for different trans packages. Careful to color trace everything if mixing harness.
The factory oem manual will help alot.
Factory ecus can and usally are wired differently internally for major model changes. The new mecal may not be the only changes for running the orginal ecu.