I was mentored by a bunch of guys who were serious target shooters for a couple years in the art and craft of building percussion target guns from old barrels and locks and whatever. Learned how to refresh rifling, re-breech, and so on. One of those old fellas was from the 1940s and 1950s era of muzzleloading target shooting, when new parts were scarce and old guns plentiful. Nobody was ruining J&S Hawken rifles - mostly guns like yours. They did it out of necessity and frugality.
I restored a true beater - no lock, no signature, crudely stocked full stock percussion rifle for the sake of learning and doing it. Then I put it away.
I’m not against doing chop shop work on guns of no historic vale or rarity other than being old. The “loss to history” of a $300 late percussion wall-hanger seems minimal. But one is better off building a gun from new parts if shooting is the plan. Until you unbreech it, you don’t know if it will take a world of work to make it shoot accurately. Re-breeching will mean getting new threads cut most of the time. Remove the drum before un-breeching. Many times they are screwed into the breech plug threads.