Hi Wiggy and welcome!
You would probably have to do just as much work as any other engine transplant as not a lot is compatible with where you are starting from.
The Mk2 / Mk3 and Corrado have the "CE2" fusebox under the dash by your feet, but the Mk4 and Mk5 are different wiring systems, so there is a bit of work adapting the engine wiring and other bits to match the car you have (unless you convert the whole car to Mk4/5 wiring?).
The ECU and engine electronics are a lot different from that in your car, as the systems are developed over time. For example; the R32 engine wants 4 Lambda sensors and the VR6 engine requires one. Then the ECU needs the immobiliser setup (or deleted).
You may be best looking for a complete donor car - if you have the space to store it.
Its all do-able but a fair bit of work.
Good luck with whatever you decide - just don't underestimate the effort, money and time these things demand.
