Spottie,
If the mag is in the gun in the pictures (can not tell for sure )then it is probably an old Tapco? metal five round hunting mag that is almost flush mount. GLWS!
It’s a standard SKS not an M or D. M or D would have a different mag release with a longer lever hanging out the bottom for AK mags. An M or D usually does not have the stripper clip slot milled into the front end of the bolt carrier. Bayo lug was probably ground off and detachable duck bill mag...