John,
Thanks for the additional information. The only markings on the stock, aside from the proof and inspection mark, are "S/5" stamped in the cut-off recess. Campbell idicates that nearly all of the M1903A1 Service rifles were actually M1903s originally manufactured with "S" stocks and subsequently altered. If DCM ordered 415 additional "C" stocks in 1935 there may have been quite a few more M1903A1 Service rifles sold by DCM that Campbell indicates. I know some of the stocks were sold as replacements by DCM - I bought one many years ago. There were some pictures posted of a M1903A1 Service rifle with sales papers on the Culverboard some time ago. I have not seen any other documented M1903A1 Service rifles.