Got Shell 93 Octane and now barely idles 1973 Dart 340

Torque converters seal or perhaps pump gasket.

I don't consider myself the best with torque converter selections, so I think you can get better advice that from me. Maybe post in the transmissions section, or see what MRL has to say. They know the torque curve of the engine and I bet would have a good idea. Make sure you tell everyone what the intended usage is.