VW/SEAT ABF, or Audi 9a will both work, and have their pros & cons depending on how you want to manage the engine.
The ABF is a digifant injection system, so will need a lot of wiring, the ECU, air flow meter etc from the donour car and so might be a bit tricky. But you could always go with K-Jet and just fit a MK2 head onto it! The Audi 9a will be a K-jet lump, as will any 2.0 lump from a Corrado or earlier Passat.
Could also throw all the injection into the bin and go with throttle bodies
The other thing you have to worry about is where are you going to put the airbox etc, as on the 16v it will need to go onto the driver side wing unless you manage to source a scirocco 16v inlet system! Fitting it on the driver side isn't really an issue, just need to modify the lower half of the airbox to get it to sit on the chassis leg.
Last of all, if you move the inlet to the driver side you'll need different fuel lines, 'Crazy Quiffs MK1 Golf Emporium' to the rescue:
http://homepage.ntlworld.com/richard.masters2/FlexiFuelPipes.htm
