The 2000-2001 Ibiza Cupra R is fitted with 4stud 305mm discs and Brembo 4pot calipers, of which you'll need 16" wheels minimum, unless you can get hold of some Compomotive MO's in 15", as I've heard they'll fit. They are pricey though.
The G60 280mm set-up would be fine for a 20v conversion as it's simply a set of discs and calipers, but if you wanted a bit more oomph then have a look for some Audi S2 calipers as they are a twin piston set-up as opposed to the single piston on the 16v/G60. The braided hoses are a must.