Any single coil/distributor system should run a ballast resistor or resistor wire(GM) to power coil when running, regardless of what is "spec".
System power when engine is running is 13.5volts to 15volts, not 12volts, because of alternator.
Ballast resistor will drop this down to about 8-9volts to prevent coil from overheating and failing
When cranking the starter the batteries 12volts drops to 10 volts, with ballast resistor as the only power source the coil would only get about 6volts, this is why you want a Starter wire for the coil that is active only when cranking.
Ford 4 post Starter Relays(solenoids) have a post just for this coil power when starting.
The "I" post, I = ignition, this post has 12v(10volts, lol) when starter is cranking engine.
Or you can add a wire from Starter Motor Post, it has 12v only when cranking, and run that to "+" on the coil.
In either I would use a Diode to prevent the 9 volts from resistor wire to flow backwards to Starter relay.
A diode is a one-way street for electricity, if you hook up 12v to one side and check voltage on the other side it will be 12v, if you hook up 12v to the other side and test again it will be 0v(or almost 0v), one-way street.
Vary handy and cheap electrical component