Since your vacuum advance doesn't work you should cap the outlets on the carbs. Check w/Langdon's on hook up once you get a new vacuum canister for distributor. That said your symptom sounds more and more like a vacuum leak at the intake manifold. Are you sure all gaskets are properly in place? I have used a length of vacuum hose to my ear and listened to the manifold at the connection to the engine/carbs for leaks (hissing sound). You can also spray carb cleaner on the joints. Where there is a leak the engine will speed up when the cleaner is sucked into the manifold. Also works for the carb connection to manifold. Have you checked mixture and timing?

Ed