The two primary circuit wires from the ignition switch connect to the + terminal of the coil. Both the wire to the distributor and your tach lead connect to the negative terminal.
When the ignition switch is in the start position, the ballast resistance (or resistance wire) is not in the circuit, and a full 12 volts is applied to the primary winding of the coil for starting. After the engine starts and the ignition switch is in the "on" position, the ballast resistance wire is now in the circuit and the other wire is not. The ballast resistance drops the voltage from 12 to somewhere around 7-9 volts, enough for running while saving wear and tear on the points in the distributor.
Attached pic is typical. It shows a ballast resistor in the "start" circuit. Sometimes GM used a ballast resistor and in other applications GM used a special resistance wire of a given length to create the required resistance to drop the voltage from 12 to 9 or so. Not sure of other years, but my '69 has the resistance wire which is easily identified by the cloth like material that covers the OD of the wire.
Port on the carb for the vacuum advance is generally just above the throttle plate. That being said, check out the previous discussion and especially JohnZ's comments.
http://www.camaros.org/forum/index.php?topic=64.0
