Setting ignition timing on a classic V8 is one of those jobs that gets overcomplicated by people who want to sell you things. The basic procedure hasn't changed in seventy years.

Start with the factory spec — it's in the service manual and it's there for a reason. Set initial timing with a timing light at idle, vacuum advance disconnected. Then road test with a vacuum gauge and a knock sensor and listen to the engine under load. Advance until you hear light ping under hard acceleration, then back off two degrees.

The vacuum advance is not a performance modifier. It's an efficiency device for part-throttle cruise. Hook it up to manifold vacuum for a street car. The engine will run cooler and get better mileage.