Bore in mm over muzzle dimension was used after 1910 but the gun is likely pre-WWI
The bore is .665" and choke .638" = .027" constriction or light full.
The shotgun chamber is very likely to be 2 9/16"
The shotgun barrel is Twist; the rifle barrel appears to be fluid steel.
If the shotgun barrel is pitted, I would suggest not using the gun with
any load. Only a smith with the interest, equipment and expertise to do so (with careful attention to wall thickness) can determine the safety of the barrel.
I do not see a maker's mark on the barrels, but there might be one on the action.
External clean up suggestions are here under "Maintenance and Restoration"
https://lcsca.clubexpress.com/content.aspx?page_id=274&club_id=43784