As you know, it will cost more to restore this gun than to buy one in good condition. In addition to the barrel work, the action will require a redo. The action must be annealed, the pitting filed away, the engraving recut, and the action rehardened. Expensive, and not at all original, with the lovely case coloring gone or at least replaced by new colors.
Since your grandfather was not a hunter, but rather used a gun as a gardening tool, I would probably follow Rob's suggestion and hang it on the wall. If you really want to shoot it, I suggest you have it checked for safety by a good double gun smith and, if it passes, shoot it as is. Lean it behind the kitchen door, and shoot vermin out of your garden with it.
Too bad. A lovely gun, and little used from the looks of it and the history you have provided.
