It can't be that dificult can it?
Surely, as you've got a complete GTI as a donor car, you can just swap everything accross, inc. the loom, brake servo and master cylinder etc etc.
It wil take a long time though.
It doesn't make a great deal of sense though? as if you tell the insurance company about the engine swap, they will bump up your premium to a similar level to a standard GTI.