FYI, the ballast resistors were used on 1.5 Ohm primary coils to allow them to function reliably on 12-volts. 3.0 Ohm coils were not available till modern materials, ie epoxy internal insulation, caught up with ignition coil technology. They used wire wound resistors in a heat resistant ceramic block in those early years. In the late 50s and on, they started using a resistance wire that didn't generate near as much heat to control the amperage to the primary coil. The 3-Ohm coil works fine on 12-volts with no external ballast.