The incoming wire to the ignition switch needs to be big enough to carry all the load on the switch, including the coil, so it needs to be 10 Ga. or larger all the way to the battery cable connection at the stomp switch. It makes no sense to have a large wire for only part of the circuit. If that concept worked, we could supply a fire engine with a garden hose from the fire hydrant to the pumper, and go with 2 inch hoses from there to the fire.
The 10 ga. wire probably IS overkill, but that's the way GM built millions of original-equipment HEI systems for 20 years or more. The wiring from the fuse block or fuse link to the ignition switch was 10 ga., plus the power wire to the coil was the same size. That was on remote-coil applications, and coil-in-cap systems, too.
Jerry
