Scott,
These bars came out in 1962. If the opposite side says "Made in Jtaly," they're before 1966. About that year the foundry corrected the misspelling of Italy. It's very strange, because there is no "J" in the Italian alphabet.
I have the "Jtaly" version stem on my 1962 Masi Special that I got from Faliero. He gave me an allen wrench for the stem that I also still have. Since I was only familiar with bars the had a hex nut, I had to ask what the allen key was for.
Michael Allison
New York, NY