I'm pretty sure that's a aftermarket stock, I remember that the folding stocks had to be pinned at one point. I did have a SKS that had a factory plastic stock, but it was set up to take AK mags. But yes, if it's a military rifle, it needs to be all original as possible.
I might be wrong but I think most of the Chinese SKS’s are new manufacture for export by Norinco and not milsurps.
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