The octane selector is not the only way to advance the timing; it is only for fine tuning. The timing can be avanced further by loosening the distributor clamp and advancing the entire distributor. I typically set the octane selector to null and set the distributor to the book, then adjust the octane selector to optimum running.
Be careful not to lift the distributor while turning it; you don't want to pull the distributor shaft tang out of the oil pump and have no oil pressure. Learned that over fifty years ago.
