All you would need is a fuel pump, injectors and take it to Vast to tune it for you. I'm running 60# injectors, you would probably need a little bigger for GT28s. They way Vast does theirs is they give you 2 files(up to 3 i think), one for e85 and one for pump, and then If you want a 3rd for valet, or race gas. You switch between the files using your cruise control stalk.
Talk to Prince or Mike at Vast, they have built a few e85 GT cars and will be able to tell you exactly what you need. They know their shit, and are very helpful.
You would basically need:
Turbos
Inlets
Vast fueling kit (injectors, fuel pump, n75 valve, rs4 airbox and MAF housing) and tune
Rods
Fueling kit might be a little differant for GT's.
Oh btw, if you buy a pre 2001.5 car, you would want to upgrade your MAFS from the Bosch to the hitachi(found on the later models). Vast has a kit, and you need to reprogram the gauge cluster. Easy stuff.
VAG-COM is your friend.
http://www.ross-tech.com/vag-com/index.html