Thanks M8, I am supprised there arn't even more. It might be interesting project.
Matt
The stats are great - engine weighs as much as a VR but has a realistic 200bhp/300lbs with bullet proof reliability and 50mpg+. Sure fire sub 6sec 0-60 (with ATB diff) and will rocket (with trailing smoke) up to 150mph. Effortless driving in everday conditions with untouchable overtaking speeds and smoother than a babies bum cruising speeds. Tuning is cheap as chips to 200bhp/300lbs with a realistic 250bhp/400lbs with a bit (alright, a lot) of cash thrown at it.
First downside...obvious...noise. It sounds awful in the mk2 due to lighter/thinner panels and less sound proofing. I'm sure for the above advantages your more than happy to put up with the noise. People look at you thinking your car is about to explode (sometimes amusing).
Now it gets more serious. You can't run stand alone management on the PD's. You have to have matching ECU, clocks and keys with a full (not engine to bulkhead but full) loom. The 6spd box is massive and requires considerable fabrication. You will have to have a dash conversion or somehow fit the mk4 clocks into your existing dash. Your dash will light up like a christmas tree with faults - ABS light, Traction control light, washer bottle refill light (as your car doesn't have them) plus others that I can't remember - you'll have to remove the individual bulbs and the beeper. Custom drive shafts will be required - passenger side is only about 6" long. As not many conversions have been done not many people can help should you need it. The TDi ECU is very delicate....slightest thing to upset it (boost, fuel/air, fuel temp etc) will put it into limp home.
If I had known 14 months ago how difficult it would have been then I would have left the 175bhp 2.0 16v in there or gone 20v. If you want to be original, different and ground breaking...then you do it without a list of procedures or help from others.
Not meaning to put you off whatsoever, but be aware of the work involved. There is a reason why there aren't many about.