Thanks for the info. My manual doesn't say anything about disconnecting the vacuum so I guess it doesn't have to be done. The manual shows a picture of the distributor with the knob in view and a hold down nut on top of a pointer pointing to a scale with zero in the middle and marks on either side of it. It just says to change the octane selector without much in the way of instructions. The knob appears to free wheel in either direction.
