Congrats on your find.
You are correct, it's a Griswold & Gunnison. What are the markings on it that might lead us to who made it? Being it's from around 1963, it could be a Gregorelli & Uberti.
Love the big bead front sight. It probably got added at some point.
Fingers (Show Me MO smoke) McGee - AKA Man of Many Colts - Alter ego of Diabolical Ken; SASS Regulator 28564-L-TG; Rangemaster and stage writer extraordinaire; Frontiersman, Pistoleer, NRA Endowment Life, NMLRA, SAF, CCRKBA, STORM 327, SV115; Charter member, Central Ozarks Western Shooters
Cynic: A blackguard whose faulty vision see things as they are, not as they should be. Ambrose Bierce