Maybe I am cross-eyed, but section 5.3 on pg 17 of the link you provided says:
' 600 SS - 640cc or less (twins up to 750cc, triples up to 680cc, Ducati 848, singles - Open)'
Anyway... I still propose changing the language of 5.1, 5.3, 5.5 to:
Engine displacement: four cylinders...