Have a look on
www.clubgti.co.uk
Lots of info on 2 litre conversions, including 8v and 16v.
I would like to do 16V one day.
3A is the 2 litre bottom end out of a F/G/H reg Audi 80 Sport, and is the same size as the 1.8.
6A/9A is the 2litre 16v bottom end (people use Mk2 Golf GTI 16V head - KR for this).
Or use an ABF out of a Seat Toledo / Ibiza 16V, as they are probably much newer cars, and you can "chip" the ECU
Cheers
Steve