Guys,
Do not elongate frame holes. The spur gear spacing is the correct distance based on spur gear mount distance formula. If you modify the mount distance you are putting your gears at risk.
The reason your head is not spinning freely has nothing to do with gear mesh, the delrin shims could potentially be a few thousandths too thick depending on tolerances. Light sanding of one of the delrin shims will allow your auto hub to spin freely.
Thanks,
Matt