The Pertronix "IgniterII" addresses the issue of leaving the ignition in the run position. I believe it costs twice as much though.

The good news is your M115 probably already has "suppressor" wires as opposed to the solid core wires used by the M110's. I just went through the PITA task of making up a set of suppressor wires for my Pertronix set-up.

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“Whatever story you're telling, it will be more interesting if, at the end you add, "and then everything burst into flames.”
― Brian P. Cleary, You Oughta Know By Now