On my 67, the ignition wire came out of the firewall and went down to a post on the starter. This was a resister wire. Then a standard wire went from this same post on the starter to the distributer. The reason it went to the start is the starter would give the post full 12v jump during starting, bypassing the resistor wire, giving a hotter spark to start. This is not needed on an HEI and most people go from the firewall to the HEI with a normal wire.
Many HEIs will still run with the resistor wire in place, but it is best to replace it in the long run. Resistor wires drop the voltage, but only when their "rated" amperage is flowing thru them. Volt meters use a miniscule amount of current and will often show full voltage even with a resister wire when checking it disconnected or with the car stopped.
Resister wires were needed to keep the voltage down so the points wouldn't burn up prematurely during normal operation when they switched from 6v to 12v in the 50's. The 12v jump would help starting, especially cold starting with the choke on.