The rulebook is right on the N2 Racing page: http://www.n2racing.org/ (scroll down).
We have Heavyweight (literbikes, etc.), Middleweight (R6's, etc.), Lightweight (SV650s, MT/FZ-07s, etc.). Then there's the Ultralightweight class (Kawi 250/300s, R3s, etc.)
We don't get wrapped up in mods...