Welcome. I agree with WIChix about the bobbin case. I'm guessing that it is probably a "1 o'clock" position finger. I'm also guessing that the needle is inserted with the flat on the right and then threads from left to right. Most of the machines from this era thread much the same way. I tried to find one very similar and I think this might help -
https://www.sewusa.com/Threading_Dia...ng_diagram.htm Another possibility is that it is a left-homing machine. You can determine if it is, by putting the zigzag foot on the machine and setting it for straight stitch. If the needle is at the left edge of the opening in the area where the needle goes, it is left homing. If the needle is in the center, between the toes of the presser foot, then it is not a left homing machine.
Janey - Neat people never make the exciting discoveries I do.
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