The Model. 12 was sent back to the factory in 59 to have the ejection port opened up and a new barrel and poly choke put on.
Somewhere at grandmas in michigan are 2 more model 12's all bought the same year , 12, 16, and 20 ga and the original barrel with 2-9/16" stamped and crossed out and 2-3/4" stamped below it.
Makes me think it was originally opened up and reamed, and then Sent back for the rebarrel later.