Quoted:
My own opinion is to lightly work on the rust with something a lot softer than the bluing on the steel - a green Scotchbrite pad, a brass brush or screen, etc. That rifle will never again be a shooter, so working on the bore is optional.
If I had it, and wanted to keep it, I would try to de-rust the finish and try to clean up the stock with Simple Green, 409, or even a solvent like paint thinner. After it was reasonably clean I would oil it up and either wall hang it or store it away. It's definitely not a shooter.
Why couldn't you shoot it?
Granted, its probably an odd cartridge, and you'd probably play hell making brass for it, and working up a BP loading for it - but it could be done. I've got a friend with a Martini I'm dieing to shoot. He spent 3 months trying to figure out how to make brass for that thing, but he did, and it works.