Not in a mk2, but a mate has a 6spd QUAIFE box and the matching LSD in his 1.8t mk1.
He got it from the USA for $11000nzd approx 3660gbp. Megabucks i know, but it is just totally amazing and damn near bulletproof!
Car is pumping out about 245bhp at the moment, and it sure as hell has legs to it
He plans to take the car up to the 280-300bhp mark.
Car is in new zealand.

Maybe you could find a 6spd box from the mk4 2.8 24v 4Motion or the S3 from a wrecker?