I done this mod on my 88 8v GTi. 239 to 280 makes sooo much difference. You need the 16v hubs (Same as the VR6 I understand) with the 280mm VR6 calipers & carriers (I think '93 - '95) and some G60 disks. The VR6 disks are the same but 5 stud!
I got the hubs and carriers from a breakers for £150 and refurbished them with new seals Etc. I got some nice black diamond drilled disks which put the price up a bit but it looks ace and stops like is should have done in the first place.
This mod wont fit in 15 inch wheels by the way. You need 16's or more.