I discovered that using my non resistor rotor creates enough EMI to disturb the advance measuring circuitry on my timing light. I had to route the pickup wire away from the ignition side of the engine in order for it to read correctly. Forget about AM radio reception unless you are really close to the station.
I'm using magnetic suppression (helically wound) wires so the resistance between the coil secondary is really low. I would guess the results would be different with resistor wires. The maker of the timing light, MAC, warns of interference issues with non resistor wires.