One source of voltage drop in the primary circuit that's often ignored is the distributor housing ground. A piece of high-flex wire like the kind used for voltmeter test leads connected from the distributor housing to the engine block will improve the ground circuit- - - -which can be pretty intermittent as the housing is moved by the vacuum advance. Normally, the ground is provided by a copper contact on the bracket that connects to the octane selector, but that can be damaged or worn out by decades of movement.
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!