M1 Carbine Stock Question

[jbm]

Hello, I recently acquired a really nice Saginaw s'g' carbine. From what I know (which is not a tremendous amount) most of it is correct. It is however in a stock that I am not familiar with. In the stock well is a S-HB and on the pistol grip is a B the butt plate has what I think is S-S3 which I have never seen anything stamped on a butt plate. Could this be the original stock for the rifle? They appear to have been together for a very long time. Thanks!