Saad:
Before you do ANYTHING to this gun, please consider your personal abilities. By your questions, I must assume you've got little experience in double gun restoration. Even the disassembly of this gun for a decent strip-&-clean should be undertaken with a measure of skill.
If you can do that without bodgering up the screws and wood, then I'd scrub all the metal surfaces with 0000 steel wool wet with bore solvent (or kerosene) to remove the rust, take the dirt and gum off the wood with a rag judiciously damp with mineral spirits, send the barrels OUT for a standard reblack, reassemble, and enjoy the gun.
Otherwise, study much, practice on something that doesn't matter, and try this one in a year or two.
Best, Kensal
