my mate does break conversions for s2s and they are awsome. ive got some on mine and they stop on a penny forget cozzy at front just do the rears. he does 300mm discs and you use your original s2 calipers but he supplies you with a set of stainless high tensile brackets,washers and bolts and they took me 20 mins to change over

so you get 2 300mm discs, brackets, washers and bolts for £130 all in and like i said they are awsome

PM if you want any more details or pics trust me you wont be dissapointed