Max,

One important implication of Glenn's analysis is that the rifle barrel will likely have British proofmarks based on the 1904 rules of proof, assuming the work was done in the UK. If you are not very familiar with the falling block family of rifles, I don't recommend that you try to take the forend off to check, but rather take Glenn up on his offer to examine the rifle and maybe collaborate with you in an article for The Double Gun and Single Shot Journal!

Regards, Tim