I have a 1957 312 Y block and I'm installing a PerTronix original Ignitor.  The helpful tech folks at Pertronix informed me via email (and I quote here): "With the original ignitor and a coil with 1.5 ohm of primary resistance (or greater), remove the resistance wire.  If the coil has fewer than 1.5 ohms, do NOT remove the resistance wire."  The tech didn't explain why the resistance wire/ballast resistor should NOT be removed if the coil has fewer than 1.5 ohms, but I think it's safe to assume it's because the coil will become too hot, creating more underhood heat, and eventually failing completely.  So here's my question: how do I determine the ohm rating on the coil now on my motor, and where do I go for a new coil if I need one that has 1.5 ohms of primary resistance or greater?  Many thanks for all thoughts.