frustrating isn't it, you just want to up grade the rotors (discs) to drilled and or grooved and they only come in the later smaller discs ( unless you pay big bucks at Racetorations in the uk.)
the smaller versions will fit, the wheel studs are the same but the pad material will over lap and in time this over lap will touch on each pad ( ie meet in the middle) and your brakes won't work.
you can change to the later discs and callipers but you will also need the later calliper mounting bracket.
i have thought of this for my racing, but then when i thought about it i can lock up the front wheels when using 185 wide very sticky competition tyres so the brakes are fine
H