Well, first off, all real RPK rifles have milled recievers- a stamped reciever isn't strong enough to hold a long, heavyweight barrel with bipod securely- thus there is no "RPK-M" or "RPK-S".
Second off, real RPK weapons do not have 16" barrels... that barrel is too thin and short to be a true RPK barrel, and lacks a real bipod (see #3 below).
Third, you can see the two stainless steel screws on the bipod mount where it is tightened to fit the barrel. These bi-pods are DEFINATELY not Chinese and not original to the rifle. A clamp goes around the barrel and then the two screws are tightened to hold it in place. Fake, and messes with the barrel harmonics.
Fourth- the saddest of all- that is a stamped reciever, not even a milled reciever, so not only is the term "RPK" incorrect, but so is the "m"!
EDIT: Yes, you can build an RPK on a stamped reciever, as some companies do with parts kits. However, no military uses/used stamped recievers for their RPK rifles, and most US legal RPK rifles are built on VEPR or Bulgerian milled recievers, not stamped (see link below for example).
http://www.gunbroker.com/Auction/ViewItem.asp?Item=42739786