^^ That thread answers none of his questions really.
Transplanting the whold thing is a hell of a job, but do-able all the same, some welding/grinding/drilling/cutting and fabricating is required to get the 4 dash to physically fit in the 3. Getting the engine to run is relatively easy doing it this way since yr nott chopping into engine looms etc and you are using the existing keys, ecu and clocks. You need to get yr hands on both full wiring diagrams to wire in the doors, boot, light and fuel system, many wire colours are matched between the 3 and 4 but obviously some arent.
Will take a lot of patience, head scratching, shouting, swearing and probably a few tears but i think it will be worth it, have considered a dash swap in mine a few times and it may still happen.
If you do it, take loads of pics
