It is indeed a Sparkbrook made barrel. Probably one of their last.

Around 1906 they were transitioning over to private ownership by BSA.

I would be taking a careful look at the chamber. The three asterisk markings on the nock's form flat signify that an armourer found rust in the chamber and polished it out. Not a major concern, but it might mean that you have a super generous chamber which could cause headaches if you were to reload for this rifle.

And, do't go scrubbing anything with a stainless scouring pad. If you don't have 'the touch' you can quickly do something that you might regret.