The drawback to this system is that if you've converted to an internally regulated alternator, or a 1 wire alternator, you'll get feedback through the 'Gen' dummy light and the relay won't close on key off. It also give you full battery voltage at the HEI, which it will want.
This will allow you to run the HEI without cutting up the harness or re-pinning the bulkhead for a larger gauge wire. Trigger the relay with the current coil wire. 10gauge wire from the battery to the relay and from the relay to the HEI. If you're concerned about being able to put the car back to stock easily without a bunch of mess, I would wire the HEI from a relay.
The black wire with pink stripe that goes from the firewall bulkhead connector, to the coil is not the resister wire, but it's also not meant to carry the amount of current that the HEI needs. If the 67's have essentially the same wiring as the 69's, the resister wire will be in the fuse block.
