John, I would say 1899 would be right. I have s/n 3400 and that is 1899.
As for the barrels, I believe they are Italian and the length is a common size there, 80 centimeters. The words mean Special Steel, I believe the S.I.R.U. should be S.I.A.U. Here is a link: http://www.ims.it/ims/ims_spa/cmscontent.nsf/DocumentsByIDWeb/5P2C8H?OpenDocument