Original ignition parts will be fine on 12 volts except there should be a ballast resistor added into the Red/green power wire to the ignition coil. Also a four terminal 12v starter solenoid with a new wire from its "I" terminal to the "+" terminal of the ignition coil. See the attached diagram.
Double check the polarity of the ignition coil. It will be / should have been reversed from when the car was Positive ground.
More 6v to 12v conversion info at this link. It was written for '55 T-Birds but will be 98% applicable for another '55 Ford.
https://www.ctci.org/battery-for-6v-to-12v-conversion/
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