OK, I'm not a gunsmith or engineer, but I do have some machining background, and some ideas on these barrels. Why not kill/remove the rust by carefully corking the muzzles, maybe with a bit of sealant (RTV silicone?) to prevent leakage, jig the barrels in a vertical position, and then carefully fill them with white vinegar for a couple of days? The vinegar will remove the rust in the pits. Flush the barrels thoroughly, run a wire brush with 4/0 steel wool through them to remove the discoloration and the sealant, then oil thoroughly and shoot forever. Just don't get any vinegar on the bluing.