Some 56's did come with a laminate stock and the 55/56's had no markings on the receiver cover. The gas block, however, does look like an earlier variation. You can find more info on this site for reference...
http://yooperj.com/SKS.htm
Live with it for a bit and do some more research before modifying it. The "Supergrade" description is just a marketing ploy.
http://yooperj.com/SKS.htm
Live with it for a bit and do some more research before modifying it. The "Supergrade" description is just a marketing ploy.