You should look into doing an Audi A4 Advant Quattro TDI swap. I plan for this to be my next project (but as a sedan rather than wagon). The TDI engines of the same era share much of the same parts with the 1.8t engine - even directly bolts up to the bellhousing and the awd system is all mechanical, so no additional work needed there. The 1.8t engines are horrible, so you can often find a cheap B5 A4 as a good candidate.