CCS SuperSport classes limit the engine mods, requiring stock airbox (which they will check in post race tech), stock compression, max 1mm overbore, no mods allowed to oem head, valves, cams, crank, rods, or cases, oem tranny, no mods to carb/throttle bodies. These do not apply to singles, twins with less than 4 valves per cylinder, and pre '94 twins.
The SuperBike classes are pretty much open, no reduction of engine size from stock is allowed (so short-stroke 748s can't run lightweight), and water cooling can't be added to air cooled bikes and vise versa. GP classes are unresricted.
FUSA rules are a little different