plugging the P28 into the adapter will cover most all. you still need to run an a wire from a4 (p28 side of the harness) to the spool solenoid.
What year is that engine? (looking for obd version here)
I assume its OBD1 because your using a P28; if so I believe you need to remove the injector resistor box. (someone check me here)

Here is a pinout of the P28 (from shortyz).



If that is indeed an OBD1 motor, get back and I will dig up what to do with the distributor plugs.

 

the motor is obd1