Yooper John's website makes specific mention of dual sling swivel mountings, the side cutouts were typically either Albanian, or post 1959 Chinese, however this note is of valid reference:
Yooper John's Gun InformationChina used both swivels during production so later guns also had bottom swivels. Rebuilds could be either.
---------- Post added at 12:43 PM ---------- Previous post was at 12:40 PM ----------
Yours looks like a Factory 306, a better image of the stamping could better ID a year.