Is there much point in doing it? I know the 20vT conversion is common but at the end of the day it's the most efficient. You can pick up a 20vT engine with all the bits for not that much these days and it'll end up being more durable, faster and more fuel efficient. The 1.8 GTI engine from a mk2 is not designed to be used with a turbo. I doubt the rods would hold the power very well...