I believe #'s in the 554,000 range were 1950 mfg.
The Date Code system started use in 1949 and I don't know exactly when in that yr.
Your Date Code would have to read '15B' to be a 1950 code.
A-1949
B-1950
C-1951
Look again very carefully and with a magnifier. A 'B' could certainly be misread as an '8' on those tiny markings applied on a curved surface.
The only other possibility I can think of is that there is no Date Code applied to that particular rifle, and instead the '158' is another of the Savage/Stevens inspection/inspector/QC codes they seemed to have been fond at stamping on their guns.
Just my guesses and speculation
