Welcome from Idaho! Nice rifle, they are great shooters. If the serial number is plain or with a "S" you should only shoot standard velocity ammo in it (or you may crack the bolt). They beefed up the bolt for HV ammo with those that are "HS" stamped.
Thanks for posting the pics!
By the way, the two screws flanking the "Marlin 39" are for mounting a tang peep sight. I have a Marbles ( apx. $120) on mine & it shoots almost as accurate as a scope out to 100Y & looks great on that vintage rifle (probably in the 1900-1920 range, Marlins records are incomplete in those years).
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