don't do it...the gti is very different. the se is an spi 1.8 engine where the gti has multi point injection, and thicker anti roll bars, thicker suspension arms, gas shockers, lower springs, improved steering rack, much bigger brakes, rear discs, 5 stud wheels. the only things similar is the gearbox and the shell
i would say buy a gti instead of making one! as insurance will be the same if not more for a conversion!! and its a fair bit of work! (the 16v conversion is even worse!!)