Picture of the flat on OP's Beretta:



The OP also took the time to produce this spiffy line drawing of what the marks on the flats look like.



Italian proof marks aren't something I have taken the time to memorize, and my last Italian gun, the 20 gauge Prandelli and Gasperini that was donated to my cause seemed to be suspiciously missing a few, including date and chamber length markings. My copy of Wernsberger has disappeared, as well.
You guys give it a try. However, it looks like this may be a 3" gun, by the 76 marking.


Best,
Ted