Learn something new every day. I was taught (back in the mid 70s) that with a 12 volt system the ballast resistor would bring the voltage down to around 9 volts in order not to burning the points all the time.

In 1953 the truck would have been 6 volt so would not have needed a ballast resistor. But if it has been truly converted to 12 volt, then it will need one whether it is built in or not.

The advantage to an external ballast resistor would be the bypass wire used to supply battery voltage while the engine is cranking, then once running revert back to what is supplied through the resistor.

But I had never put the numbers to do the math. Thanks