its getting it all wired up that will be a pain. My mate in his mark 1 gti put a digifant 8valve from a mark 2 in, but he had to get the wiring done and the only place wo could do it were dubsport who over charged him and did a crap job (electrical tape everywhere)
If you just want a replacement enigne then why not just get hold of a 1.6 driver engine, just goe straight in, no major wiring to worry about.