There have been a few Sino-Banian imports seen fresh in grease with the phenolic stocks. It's definitely not widespread though. I've seen 1 or 2 out of many thousands of imports. As for old imports (this one with that stamp is definitely a pre-94 import by the way) I honestly do not remember seeing any recorded with phenolic stocks, but that doesn't really mean much because I haven't seen a lot of things!
They very well could exist, and possibly in quantity.
It's a nice gun, those blade stocks with the wrap around rear sling swivel are some of the nicest out there. The mismatching magazine is pretty minor in that the stock is obviously mismatching as well, but both those certainly put a hard ceiling on the price where collectors are concerned. I'd guess somewhere in the neighborhood of $400 to possibly even $500 when sold to the right bidder in today's market.