My m99 doesn't have a serial number. I searched the web and found that Marlin stamped the barrels with a two letter date code before 1968 GCA. Don't have it in front of me but I think it's stamped AK which translated to 1967.
Found it. Here is a link.
http://marlin-collectors.com/forum/viewtopic.php?t=2288
Last edited by ring3; 02/22/17. Reason: Added link
