as you can see the motor is in my car and has been in for a while I just haven't been able to devote time to the harness. My WRX takes priority lol.
It's fairly simple the first thing you want to do is sort out what you don't need to use in wrx harness and what you do need.
then you will want to loom as much of the wires that go to the same direction together.
You will end up with alot of wires... but what i have found works is that you cut and separate the wires that have crazy routes and make then as clean as as siimple as possible.
Try and weed out as much of the non engine related wires as possible.
Once you have both cars ecu diagrams and it should be a simple cut a tap situation since they alot of common sensors. Some are not so common too though.