If the firearm has sentimental value, I'd say leave it as is, and buy something else to shoot. BP is hard on a firearm, and a forgetful few days after shooting but before cleaning can do alot of damage.
If you want to shoot this one, I think you are much ahead by buying a pair of modern locks and modifying the plates to fit the stock recess. You may need to do some adjusting of the hammers by bending, but if the throw is off, you will need to do some welding. If the original lock screw placement interfers with the modern mainspring or internal bolster, you may need to reposition these hole locations, but that is not a tough job.
If you took the locks to a tool maker in a shop with CAD capability, they could make make a beautiful copy, with modern metalurgy and heat treating ... but wait till you see the bill!