Excessively advanced timing is an interesting thing.
A vacuum advance unit under light throttle (thus deep vacuum) can advance the spark WAY beyond what would normally be considered appropriate. Under these light load conditions engines generally get better mileage with more advance.
As you step on the gas the vacuum signal drops and the timing is instantly retarded. Kinda slick for an "old school" technology approach!
Modern method is electronic advance using engine sensors. Of course I know all you guys are smarter than a "computer" or an old fashioned vacuum advance unit,
So,,,,,dial away on that MSD box!
Ernie
PS Hey, just something to think about.