I have no personal experience with this but here's what I've learned from this board and a get-together or 2 with other TDI'ers:
This conversion requires an "AHU" engine from a B4 Passat (1996-97 in the US) or an A3 Jetta (1997-1999.5, older body style) as it has the same motor mounts as the older A1 and A2 style VWs. It's a lot of work, as mounting places have to be found for sensors, ECU, etc. as the fuel pump for the TDIs is controlled electronically instead of by cable as with the old Rabbit diesels. I saw a TDI-powered Rabbit truck at one of the TDI GTG's last year. The owner was using the was using the A1 transmission in the pickup, but I don't know if this was by choice or necessity. It would seem best to install the A3/B4 transmission along with the engine, as it's built and geared optimally for that engine.
I've heard that some people have put the older design IDI 1.9 VW diesel in the A1 VWs. While this engine doesn't quite have the performance of the TDI engines, it's a much easier retrofit into an A1 than the TDI. There may be a turbo version of these available, but I'm out of my knowledge at this point.
Good Luck!