I actually have no idea, but from experience in the class I'd suggest 21/60 (2.86) to start and go from there.
Whatever your driver, shoot for that ratio and have 2 teeth on either side for the axle. You should have what you need.
We race on Summit Point Shenandoah, Summit Point Main and VIR North Course. 2.86 is a good middle starting point for all of them.
Have fun,
Clark Gaynor Sr.