How about you leave it as it is, but...
Have a horsepower limit? (hard to enforce)
or,
Have 3 classes, 583, 675 & 620.
If you split it in to 2 classes, then not everyone will have cash to spend on headwork or whatever to compete with a 620, and if you say no headwork, then the 583 riders will be miffed coz they can't afford a BB kit.
Otherwise, I think it's pretty good for a first attempt.
As for it being a novice class - No way!!
It's a race series for DSC members - not novices.
2p