Classic case of a frozen advancer. The points cam is hollow; springs rotate it around the advancer core (bored to fit over and bolt onto the camshaft). Years without proper lubrication and cleaning will cause the advancer to jam.

Remove points plate. Remove cam bolt and washer. Pull the advancer, its indexed to the camshaft by a small metal pin. Soak advancer in WD-40, penetrating oil such as Kroil or diesel fuel. Working it a little at a time, unstick the advancer and ease the springs off. Get it apart and wiped clean. Might need to clean the sliding machined surfaces with Scotchbrite pad and WD-40. Lubing lightly, reassemble all moving parts with high temperature grease such as used for ceramic disk brakes. Note the points cam needs a different lubricant.

Align points cam notches with base plate slot, to eliminate the 180 timing out-of-phase problem.