Nick I can't say for Lithgow. However we run Todd Road, Oakleigh, Morwell and Pucka and Ballarat, the gearing ranges from 11-80 to 11-82.
I havent seen many tracks that vary from that.
11-81 is a good starting point
Out of the box supplied is 11t. Everyone puts a 10 on which also allows a smaller rear sprocket to be used and much less chance of tearing up chains and sprockets. Oakleigh , Todd Rd and Morwell all use 10/80 - 10/84 range.
yeah most people I know run a 10T front and around 81 rear. I'm the odd one out that runs an 11T front. I think we had 11/84 at Lithgow when we there. Didn't win C9, but was faster than a few C12s.