If there are any parts you believe you are missing, just call up Hahn and I am sure they will send them to you free of charge. When I bought my kit way back when, some stuff was in fact missing, and they sent it all in a timely fashion.

For the return line, there should be a section of fuel pressure hose that runs off the regulator, and then connects to a hard steel line that runs under the length of the car. As it is under the car and exposed to road debris, I suggest you use a hard line.

The oil pressure line that goes from the sender unit to the turbo is steel braided hose with AN fittings on both ends.

Of the 4 holes on the turbo, only two should be open, oil inlet and oil outlet. The other two should have brass plugs. If not, Hahn simply forgot. Their kit does not include the parts necessary for water cooling, but yes, it can be done which is nice.

1999 Eclipse GS
Built motor
Hahn 16G Turbo w/ FMIC
Hahn Stage 5 Portfueler (270's & 500's)
Zeitronix Zt-2 wideband w/ 3.5bar MAP
3" SS Turbo Back
CM Stage 4 Clutch and Fidanza Flywheel
Baer Big Brake Kit