Welcome Larry. A Research Letter would provide the gauge, DOM, original configuration, and to where the gun was shipped
https://lcsca.clubexpress.com/content.aspx?page_id=22&club_id=43784&module_id=245742

If a 12g the chambers would be (unless otherwise marked or after-market lengthened) 2 3/4"; 16g or 20g could be shorter and need to be measured, as does the choke constriction.

There is also a great deal of information in the FAQs
https://lcsca.clubexpress.com/content.aspx?page_id=274&club_id=43784

ANY vintage double deserves a check and clean by a qualified double gun smith before use.