The distributor cap and rotor are different (taller) on the engines that ran 12 volt ignition systems (late 55 to 62) The low height caps had a tendency for the higher voltage spark available with 12 volts to flash over from the tip of the shorter rotor to the distributor housing, particularly if a plug wire came off and allowed the coil to develop its maximum open circuit voltage. Either use a short rotor with the cap you have, or buy a 55-62 distributor cap to match your tall rotor.
Jerry

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