tneely. Hold on here. Wait a minute before you go buying anything else and wiring anything else. Lets confirm more info.
1. You have a 53 motor with a 6V starter with a solenoid mounted on it and a 12V system?
2. What kind of ignition switch do you have? Do you have the spring loaded one or just an on-off ignition switch with a separate push button somewhere?
3. Does your coil say internal or external resistor? Hopefully an external resisted if you have a ballast.
4. What is the part number of the coil you are using and what does your ballast resistor look like.
5. BIG QUESTION...ready? Have you been driving this truck with no troubles? What happened before "I explored my ignition system more today and it is still perplexing."
Also, I am not sure yet if you have a bypass* system. It is best to have a bypass system.
I will watch for your answers and help you. Lets back up here though.

There is a good write up in the tip section on 12V conversion. Do what it says. Jerry is pointing you to the bypass system with his suggestions.
Ballast resistor
Coil
Without an R terminal I don't think you can use the ballast system. Get a solenoid with an R or I (this terminal will NOT be a screw, it will be a stud with a nut.)

Right is right, even if everyone is against it, and wrong is wrong, even if everyone is for it. - William Penn