SKS-M uses AK mags with AK style mag release, 16.5" shortend barrel, a neutered bayonet lug, and date specific serial number (93 or 94 prefixes).

This looks like a standard pre-ban, Type56 with an aftermarket, duckbill hi-cap magazine. 1976 triangle arsenal guns will have a serial number beginning with 21. 1977 triangle serials will begin with 22.