Tommy you could be right might be the Armourer's mark.I found this though it deals with M1 Garand it makes a note about marks.
EB:Elmer Bjerke was promoted on January 6th, 1947 to Forman of small arms inspection at Rock Island Arsenal. He was responsible for the final inspection of new and overhauled small arms. He served in that capacity until 1958. All small arms inspected under his supervision bear the markings "RIA" for Rock Island Arsenal and "EB" for Elmer Bjerke.
Frank Krack was Assistant Foreman of the Inspection Division at Rock Island Arsenal from September 17, 1941 until he retired on July 19th, 1946. During that period all small arms inspected under his supervision would be stamped with his initials "FK" as well as those of the Rock Island Arsenal "RIA
Arsenal overhaul and inspection stamps
Now if I can find out who was in charge of RRA in from WWII to 1960 might be his initials?I have another thought the the gun came in a RIA box must of been how things were sold to the public you know central store front to say?