Check the voltage applied to the coil + terminal during cranking. I'm going to guess it's too low to trigger the Pertronix module while the starter load is on the electrical system. A 55 International pickup I worked on had a similar problem, and the culprit was a loose, dirty connection at the back of the ignition switch that was dropping the voltage applied to the coil. It had a regular point-type ignition system, though. What happens when you try a 12V boost start, or crank it with a battery charger attached? Does it fire up normally then?
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!
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