The Blue Book says the Marlin 80-C was made from 1940 to 1970. A Glenfield economy version on the same action should have been marked 80-G, but I figure they were not too careful about their markings when an order came in. Does yours have Microgroove rifling or standard? Had to have been made before GCA 1968 to lack a serial number.
The Marlin was about $42 in the middle '60s, the Glenfield $35.
Interestingly, different sources give different magazine capacities, G&A says 9, GD says 8, cheap replacements from Numrich are 7. Unless you just lucked onto a real Marlin magazine, your only sources of spares would be Numrich, Tom Forrest, or maybe Triple K.