Dan, if it were me, I would get keith to redo the hub for the 6-bolt pattern then you wouldn't even think twice about a prop slipping. You can insert a "shim" in the hole to get the i.d. to 10mm. You should have easy access to a machinist where you work now for doing the props. The other angle to prop slippage is that the old CH ignitions that Keith used has a bad habit about being out of time. I still remember the "flap" I received in my heavy leathered gloved right hand when I started Mike Donovan's BME 102 and it backfired!! The new iginitions Keith uses not are much more reliable.

Bobby