The shotgun you see here is the only over-under I consider to be both vintage and American. Even this Superposed was made in Belgium, it was designed by John Moses Browning — one of America’s most famous gunmakers.
This 20g is coming up in Poulin Auctions Spring 2019 sale, being held 3/30/2019 – 4/2/2019.

Lot 1172: BROWNING SUPERPOSED O/U SHOTGUN: Cal. 20 Ga., 3″ Chambers. S#15017. Bbls. 26 1/2″ VR w/ white front bead & mid-bead sights. Choked skeet & skeet. Mfg. in 1959. Single selective trigger. Blued steel action & bbls. LOP: 14 1/4″ DAC: 1 1/2″. DAH: 2 1/2″. Weight: 6 lbs., 5 oz. Gold washed trigger. Checkered walnut round-knob pistol grip stock w/ red recoil pad. Checkered Lightning style walnut forend. Long tang trigger guard. CONDITION: metal retains 70% original blue w/ significant finish loss on lower tang, forend release & action bottom. Action sides show fading & bbls. Exhibits a few light scratches w/ one scuff on left side of top bbl. Trigger finish is faded overall, but w/ gold color still visible. Wood shows added finish in some areas & finish loss in others. Scattered sm. scratches & compression marks appear overall. The left side of forend shows one 1 1/4″ gouge. Bores bright & shiny. Estimate: 800.00 – 1,300.00 USD