Does it have the prefix FW S1-S56800 from the L.C. Smith Gun Company from 1946-1950 or the Marlins Firearms Company FW M56801-M59152 from 1968-1971? The high rib (Single Sighting Plane)started as an option in 1939 for $5.00 extra and in 1940 became standard. I have a 12 ga. L.C.-Marlin era 1946, high rib that also doesn't have any thing stamped on top of the barrels, but has Armor Steel on the bottoms. Serial number FW S1825. I believe that all shotguns manufactured during the Marlin takeover were Featherweight models till the end. I'm sure if you post the serial number you will get the answer.