USGI Bob,
I believe yours is a number 50, not 30. We've been playing with your picture here, but note my quote is a typo, mean't to say "I now believe it to appear to be":
“50†marked stocks - The Carbine Collector's Club
Bruce,
Main objective here is a number or numbers near the Recoil plate. It's the actual number stamped that we're trying to gather the meaning of. The other information IE: serial number, if import marked .. etc is secondary, but still hoping to gather input.
To Add: Free to report on any observed carbine or loose stock, even if seen online auctions , gun shows, etc.