Hmmmmmmmmmm... they sure put most of the impression on the left side (the beginning) of the stamp they used to make the Lever Boss Code.
The left side of the
OVAL around the LBC made that initial deep impression on the left side of your rifle's partial LBC... and after looking through my extensive LBCs in different years, I can only come up with what it might possibly be.
My best guess is that it could be Inspector #11 who seemed to do a good many of the LBCs in 1958 and 1959 (see bold face excerpts below) since the 2nd vertical line might be a partial impression of the 2nd digit of his #11 Inspector's number. But without the letter indicating the year of manufacture, it's anyone's guess.
J= 1958: 950xxx, 9494xx (?J) 9512xx(J),
955xxx(11J), 95794x (J), 95896x(9J)
K= 1959: 9593XX(9K), 9610XX(K),
9613XX(11K), 9637xx, 961731,
963837(11K), 964xxx, 96556x, 9677XX(8K),
Sorry I can't be of more help...
Strength & Honor...
Ron T.