I think I have discovered the meaning of the W.L. in the oval cartouche. I believe it is the stamp of the stocker during the manufacturing process while the rifle was still being assembled in England. An abbreviation of W.L. Sargant. Apparently the process of assembly went something like this:
Barrel made at the London Armory and proofed; Lock and other parts made by various Birmingham hardware manufacturers; Parts sent to the stock fitter or assembler. Finished rifle sent to the exporter (Sinclair Hamilton and Co). I would think that guns shipped to the South after a certain point got the JS Anchor stamp once the weapon was inspected on the other end of the shipped received end.
Photo found on relicman.com
Private Watkins. I hope you are able to load some more photos or your rifle. Are any of the assembly marks still visible on your rifle? Check the ram rod channel on your rifle for other marks.