John,

That's a excellent photograph of the right side of the gun. I knew that the M57 had a thumb safety added to the gun at some point early in its history. I also believe that both versions were available through some of its manufacture. What I have been unable to determine is when the safety was introduced. Your research says 1959. May I ask where you learned that date?

One interesting thing is that all of the reference books I have about the M57 show it without the manual safety. Remling's book even has a drawing of the M57 with a short (standard) grip, but I think that is just an editing error. A photograph in the same chapter shows the (correct) longer grip.

The one disadvantage to the gun is that the longer magazines are pretty scarce, and therefore expensive.

Regards,

Buck