i looked into this the other month, Hi-spec do a 4 pot conversion to fit behind the 16"s (300mm disks) brembos youll need 17"s to fit the bigger calipers, AP Racing do an race kit but its not dust sealed no not to great for road use unless you wanna be cleaning your brakes every week. I very good friend of mine used God speed and ended up in a legal battle with them, they were so bad it was untrue, the calipers were old volvo 1s which had bee widened! he ended up with a set of 6 pot Tarox and couldnt sing their praises enough!
Ive decided just to uprate the disks and pads, dont fancy locking up all the time!!!!