Everything from one car into the other, all the loom from the front to the tail lights as well. Even the fuel tank is different. There's a difference in the bodyshell from around 98 onwards. If both cars have the early style dashboard you're ok. If one has the Forester type dash with 3 glove boxes you're in for some surprises. The wiring loom inside the doors will often have different plugs too so you may need to swap that as well. Do not discard anything from either car until the project is 100% finished.