The serial number on the butt socket above "BSA&Co." is not original as you probably know. I believe it would have been only on the receiver ring (and of course bolt) originally.

An early aperture sight was fitted from the relief cut into the wood ahead of the butt socket, and the two holes were drilled and tapped for the SMLE safety spring holes that were normally used for that type of base. The type in this photo at the bottom perhaps: http://forums.nitroexpress.com/showflat.php?Cat=0&Number=151057&an=0&page=0#Post151057

If you take the rifle out of the stock, the two digit date of manufacture may be stamped into the bottom of the barrel similar to this "95" date.