As far as i am aware you can't. I asked a main vw dealer about it 4 years ago, and they told me the gti system was too large in diameter, or something to that effect. However that was for a 1990 1.6 driver, i presume yours is a 1991/2 model so the result may be different. If not i suggest a nice discreet DTM twin pipe conversion, suits the looks of the mk2 almost as well as the gti system, and will be nice and throaty to boot!