I think in a situation like this, there would need to be so much cleaning on different levels that you would remove more of the historical appearance that I would just leave it alone for now, as Mark said, and clean the bore out as well as you can, make sure the bolt functions well and take it out and shoot it!

Do check the bolt and chamber out after a thorough cleaning. If any questions, let us know.

Maybe the next owner can work to try to restore it better. I would disassemble the thing completely and replace a lot of parts if I ever wanted to restore this treasure.

Enjoy!