Thank you for the responses and links. I was able to see the bobbin case differences and confirm that I have a matching set.
For 306 users, does it matter which direction the bobbin is loaded into the carrier? Should the thread change direction as it exits under the carrier spring or not? I mean, if the case has the open side towards you and the spring is pointing counterclockwise, should the bobbin be loaded with thread clockwise or counterclockwise?