I would love to see this happen, been looking at some Mk3 diesels which have been boosted and they have hit around 160bhp with lots of torque to back it up.
The PD engine is much more efficient and i think can be pushed near to 200bhp safely.
I am talking completely of the top here but I would think you would need a lot of the Mk4/audi donor car and a bunch of bits from a std Mk3 diesel and some bits of a 16v/VR6 petrol.
Mk3 bits are cheap as chips but not sure on PD engine and required extras, also custom parts for exhaust system might be hard or £££ to find
I am sure someone will put you right on exactly what you need then its a search on the net to price it all up
