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I have an old barnes safe at home (dated 1867 on the cover) very similar to yours in the pic. Previous home owner left it for me and left the door open without the code.
Remove the panel on the back of the door and watch the tumbers line up and write down the correstponding #s on the dial. Just remember to note if the dial is Left-right-left or right-left-right when doing the combo. be sure to test it a bunch of times too.
Its also very easy to change the combo too, you will see.
Jeller