This photo shows an upper rotor shaft that has been modified to provide a reduced travel length for the slot. Originally the slot allowed for a total mechanical advance of 20° in the distributor - 40° at the crank. This would correspond to an old factory motor tune that called for static timing of 0° at idle with one of the two springs being very heavy.

This one is reduced to 13° (26° at the crank) so that an intial static timing of 10°/12° will sum up to 36°/38° at the crank.

The cam was removed to fit a Ford Druaspark II reluctor onto the Autolite distributor.
Steve Metzger Tucson, Arizona