From my experience with the Baikal combo guns, the windage can not be easily regulated on the Baikal. EAA, the importer. could not adjust the .223 windage on a 12/.223 combo gun.
I dont know of any gunsmiths that specialize in regulating double rifles, drillings or combos.
Also, I always sighted to the top barrel then adjusted the bottom barrel.
Good Luck