Many years ago I had some limited luck using a Pink Pearl ( I think that was the name) eraser or using brand new #2 pencil erasers if they were soft and pliable. They removed some ink stains / marks from baseballs reasonably well if they were small without affecting the surface of the ball. With a vintage ball such as yours and with black ink I have no idea if this would work. Also since the ball is vintage and somewhat colored it may create white spots on the ball where you use the eraser, also it may roughen the surface of the ball also.
Good luck.
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