like i said - once you bring EJ20G engine loom through the firewall you only need to *splice* into a small number of wires in the original impreza wiring. I think I only spent less than a day on this an nowhere near 40 hours... in my driveway. It's not very complicated at all. You just need to make sure you have enough "engine loom" wires to make it into the car. This may require some sorting out. It's not bad - especially if you have the hole in the firewall for the AC. The AC kinda makes things more complicated.