Beginner,
Real.
Right side SG boxed and crossed cannons is the primary contractor who received and assembled the carbine. Markings in slingwell in the manufacturer of the stock, but the 39A was added by Saginaw.
Ref: CC newsletters, War Baby.
Depending on how in depth you want to get into carbines, and we are all still learning, there are some good options. You can join the The Carbine Club - A CMP Affiliated Organization They put out a newsletter, and you can purchase back issues. And or buy some good books. War Baby and War Baby Comes Home by Larry Ruth, go into detail where others like U.S. M1Carbines, Wartime Production by Craig Riesch is more of a quick reference and parts markings.