"Pulsing" voltage, RPM drop with load.

JoePole1 said
Measurements at battery terminals, engine off.
Everything off 12.6V
Headlights on 11.9V
Brake lights on 12.0V
Brake lights and head lights on 11.8V

Maybe a slightly discharged battery but OK.
Your car has side marker lights so lights on the load is slightly higher than a '67. Therefore that they pulled the battery down a little more than Dana's is not surprising.

JoePole1 said
Measurements at Cigarette lighter , engine off.
Everything off 12.4V
Headlights on 11.2V
Brake lights on 11.9V
Brake lights and head lights on 10.9V

Same as above. Resistance in the circuit. Since you've interconnected the battery and alternator feeds, the resistance is either shared (such as battery to stud on relay) or its in both the alternator and battery feeds to the main splice.

JoePole1 said
Measurements at Cigarette lighter , engine cranking.
Everything off engine cranking 10.6V
Everything off engine running at idle 14.7V 850 RPM otherwise car was last running yesterday.
Engine running at idle headlights on 14.0V
Engine running at idle brake lights on 14.5V
Engine running at idle headlights and brake lights on 13.0V

Need to be looking voltage drops and checking for whether the voltage follows the rpm.
Going from 14.7 to 14.5 and 14.0, is OK but then the big drop to 13.0 doesn't make sense (if rpms were the same). Another variable we don't know is the battery charging rate. But it should have been highest immediately after starting and then drop quickly.

JoePole1 said
Voltage at alt is 12.75V but I measured this after warming up the car. It was also 12.75 at battery

??? Do you mean after you shut the engine off?

JoePole1 said
Remember that I ran a 10ga wire from alt output to starter relay with fuse link.

You should get the exact same results with the wire removed. The only difference is the ammeter will show the amount the battery is charging when the engine is running.