6 cylinder tach wire firewall hole location

[RichardJ]

Instead of punching unnecessary holes in the fire wall, get the correct Packard connector terminals and use unused slots in the firewall/bulkhead plug.

The existing wire for the Dist power is the cloth covered wire in this image. That wire is a Nichrome resistance wire that the guys converting to an HEI dist are so deadly AFRAID of.
That resistance wire terminates inside the harness wrap, along the side of the valve cover. At that point, the resistance wire is spliced together with a wire (typically Yellow) that goes down to the starter solenoid and also another wire (copper) that connects to the coil.