Dont need to mess about with the loom, simply swap all the old engine bits over from the old engine. The lump & head is basically identical underneath all the gubbins.
1. Unscrew the fuel injector inserts and swap them over, you need a large allen key. Oh and fit new injector seals while yr there, dirt cheap from GSF

2. There should be a WUR on the front of the old block, unbolt this along with the mounting bracket & swap.
3. Swap the dizzy over
4. Can use your old gearbox or the one off te digi, whichever is in better nick. Put a new clutch in, and replace the input shaft seal, and the pushrod bush & seal.
5. The coolant flange on the front of the engine is different, if your old one is metal get a new seal and fit to the PB head, if its plastic get a complete flange from VW and swap the old sensors into it.
6. Rocker cover is also different I think, get a rubber gaskit kit from VW, it comes with new studs so swap those on as well. Oh and if it has a PCV valve on the old engine, get a new bung for it. Think this may only be for Digi lumps tho...
Edit: gotta be more I've forgot, but you'll see whats different when the time comes
