Hi Stuart,
I don't see a resistor in the wiring diagrams and have never seen one on a 6 volt system.
If you look at the way a resistor is wired into the system you will see that it is in series with
the ignition terminal on the switch and the primary winding of the coil.
This can only drop the amount of voltage going to the coil.
When doing a 12 volt conversion a resistor is used to drop the voltage to 6 volts for the original 6 volt coil.
If you replace the coil with a 12 volt coil you would still use a resistor to drop some of the voltage because
a 12 volt coil is actually designed to run on approximately 8 volts.
