71 Dodge Dart Swinger in England

Next question ignition timing . I've read set at 0 BTDC static. At 800 rpm should be about 8BTDC with vac disconnected and at 3000 rpm 36 BTDC with vac connected. Does this sound correct?

Running at 800 rpm and 8 BTDC it not idling correct i can hear it firing in the headers ( sounds like the manifold gasket leaking) if a retard it further ( turn dizzy anti clockwise) it will run better, But if I go too far its then hard to start. Just I thought at this point i still have the dizzy vac disconnected, maybe this should be connected to the manifold so it only pulls the timing back when running?