I have been looking at GTi bodykit parts and how many differences there were as I have a bright red TDi, now got GTi 18s on it and people do mistake my car for a genuine GTi (the uneducated).
From what I can tell, the front grill should swap over no problems. The headlights are slightly different inside but essentially the same outer unit.
The front bumper is totally different, its actually got wider buldges at the outer edge of the headlights and bigger appetures for the foglights although the centre section does look like its similar to the rest of the range.
Its got a different front splitter under the bumer and also some stick on side sill covers.
with my mk3 golf, gti look wad achieved with an arch kit and some slot in bits. Unfortunately with the mk6 its a case of changing some real big bits!
I think also the read lights are slightly tinted, its got a different rear diffuser (which I think can just be unclipped but I havent looked yet) and different rear exhaust.
Its also got a clip on bigger rear spoiler too, which back in the day you either had one or didnt, now its a case of you have one or you have a bigger one!
The gti is also an Inch lower than the rest of the range and the GTD is about 1/2" lower.
Think thats all the differences, I so dont fancy changing the front end on mk6, could be a big job!