The only way a 1901 rear sight would be properly used on an 1896 carbine would be if the stock had been replaced with the 32" long M1899 style, which yours has not.

Apparently "Bubba" (he sure does get around) was one of the previous owners of your gun, as SA would NEVER have made a modification such as you describe.

While your exact number has no surviving data, it is right in the midst of many other carbine numbers. The stock date matches the SN. The wood patch is plugging the cut for the sling ring bar.