Here are some pics of a North Vietnamese SKS I managed to acquire. There's no paperwork or documentation to go with it but as far as I know these didn't come from anywhere else but Vietnam and no one has ever seen one with an import mark. She's all matching and has seen quite a bit of use but still retains the original sling. There seems to be a divide among SKS collectors as to whether these were actually produced in the North or made in China and shipped in. In any case production seems to have amounted to about 10k units and , I believe, ceased in 1965 which coincides with the beginning of US air ops against the North. Here are some pics.
Nice rifle! This item doesn't need papers to authenticate. (One of my major frustrations lately has been the inordinate deification of capture papers to authenticate.) And yes, there have been major arguments on a couple of the firearms boards as to where they were manufactured...