It sounds like you would receive more enjoyment from the gun as a shooter versus just the current caretaker. And there is nothing wrong with wanting to restore an original muzzle loader of moderate value into a safe shooter. I've learned that most things are doable given enough time and money put into the project. But in every case, there is often a point of no return. So, if you are set on trying to keep it in safe shooting form, I would send the barrel to Bobby Hoyt for his inspection. He will be honest with you if the barrel can be repaired to "safe" shooting condition. And I trust his judgement. He has restored a number of barrels for me. And, what all would be required to make the fix. If, in his opinion, he recommends retiring the barrel, you still have the option of having him make you a new barrel. Especially while your barrel is already there. He can duplicate the outside dimensions of your barrel exactly, in case it's different than whats commercially available today. And you can pick the same or different caliber. That way, any good muzzle loading gun builder can refit the new barrel to the stock with minimal fuss. And install a new drum so the hammer hits square on the nipple, shape the new breech plug, install new sights (or use your originals), etc, etc. I would think this would be preferable to cutting off breech plugs, shortening fore stocks, and re-working barrel channels. And, in the long run, probably the least expensive route. And you still have the old barrel for display. Just some thoughts.
Rick