Since the vacuum advance only functions at very light-throttle cruise, it's pretty forgiving if it's a degree or two off. As soon as the throttle gets opened to accelerate or pass, the extra advance from the vacuum unit goes away and only initial and centrifugal advance is in play.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!