i just bought some mk4 golf callipers, these bolt straight on, you use mk4 pads and mk2 discs, i got a post 90 mk2 gti so the handbrake cables are the longer ones i think im right in saying, and these hook right up. all that is left to do is source the flexi hoses as the mk4 callipers have a different connection.
you can also use mk3 callipers... but if you do search there are pages on this one.