Making brakes worse?!

hi all,
basically ive just bought a mk 1 gti with a mk2 engine 16v. the convertion was done very well and evry thing is sound. its currently fitted with a 280mm brake convertion and it stops really well. however i want to put a set of 13"ATS classics on it and these wont fit over the disk i was thinking of goin wilwood calipers on 239 drilled and groved disks will the calipers fit? ive go a mk2 master cylyinder and goodrige hoses. im guna do the rear disk convertion eventually. how much will this cost for the front convertion has any one got any tips for the best set up.
this also means ive got a big brake kit up for sale with brand new brembo disks and pagid pads still in the box i would preferr to swap with an equally good set up thanks
ed

i have standard mk1 calipers and carriers if you want. i think they do a 249mm wilwood kit for the mk1 to fit over 13"rims. about ?500 i think. don't bother with rear discs unless it's for show.
ultimately, bigger discs give better leverage.