408....409 mystery. I agree it doesn't look like any other 409, but remember that '09s were a decade+ into production when this gun was made, so that argues against it being a prototype.

RE: firing pin holes, I just had Rich Cole do some minor work on a 1939 Beretta 410, he said he filed down the firing pins to better match current production primers. But I don't know what spec he's following.