Welcome. Congratulations on an interesting gun. Post some pictures when you can.
No one can tell you over the internet what ammunition may or may not be safe in a given gun. That requires a qualified double gun smith with the proper tools and expertise.
That serial number is circa 1910. At that time, the heaviest 12-gauge loads being offered by our North American ammunition manufacturers was 3 1/2-drams of bulk smokeless powder --
ARROW 12-gauge, 2 3-4 inch, 3 1-2 drams E.C., 1 1-4 ounce.jpg
or 28 grains of dense smokeless powder (such as Infallible or Ballistite) --
RECORD 12-ga 28-grains Ballistite.jpg
pushing 1 1/4-ounce of shot. Those 12-gauge loads could be had in 2 3/4-inch or longer shells.
Some DuPont powder booklets from the 1920s/30s show these loads had pressures above modern day SAAMI specs for 2 3/4-inch 12-gauge shells.