This is purely opinion on my part, but the SKS was created in Russia, and made there for a number of years before the Chinese began manufacture. The Russian SKS tends to have better quality machining...
The website surplusrifle.com has good information on MANY different rifles and pistols, including the SKS. Follow instructions on field stripping, and use the supplied cleaning rod and parts. If you...
The RUSSIAN SKS may be date marked on top of the receiver cover (properly called the rear housing) , along with the symbol of the arsenal that made it.