the basics you'll need are:
- kkk k03 turbo from a 1.8 20vT passat
- rothe motorsport k03 manfold (or a copy from german ebay)
- rothe turbo downpipe for k03 (or a copy from german ebay)
- g40 exhaust manifold gasket, k03 to manifold gasket, k03 to downpipe gasket (all stock VAG parts).
- forge motorsport uprated actuator for VAG 1.8 20vT (standard one is designed to work with an N75 valve which a G40 doesn't have).
- oil feed and drain pipes
- oil drain boss welded onto sump pan
- dump valve of some sort (stock vag recirc is the best type for these turbos)
- front mount intercooler & pipe work to suit (depends what you can fit on the car)
- the turbo is water cooled so you need to tee into the water pipes for the supply and drain from the turbo. So you need some bits of pipe, some t-pieces and some fittings for the turbo. You'll have to just figure this out when you got he turbo on the car and can see which water pipes are nearby to do this.
- ...probably a hundred and one little things I've forgotten about....
Then on top of that you really need to get a turbo-specific ecu remap, ideally a custom one with rolling road time. Depending on how much boost you plan on running you may need a different MAP sensor which will require a custom ecu map to suit.