Misfit:

If we are thinking about the same screw, the one that holds the rear bearing to the cam, I think that was probably the most often replaced part on all the rear cam OS engines. People, trying to take it out, would tighten it and break the head off since it's a left hand thread, and instead of loosening it, it got overtightened and broke. I don't think anyone broke the second, though.

If you have, or have access to a small lathe that will buth cut metric and left hand threads, most likely the esiest thing will be just to make a new one.

Sorry I can't give any more encouragement.

Bill.