The gun in question looks to be one of H&H early hammerless guns, and judging by the fences would have been made as a shotgun.

I suspect at some point in the last 140 odd years the original barrels became damaged / worn out and it was just an old gun.

So somebody rebarreled it.

This is the sort of gun that generally obtained for not a lot of money as it is far from original, yet can still give a smile on your face. Guide price - I would have a look in the auctions for forend and action only.

If the action is sound and unmessed, this might be a candidate for a new set of barrels. It will cost several thousand in whatever currency, probably five figure of thousands. Done properly you could have a lovely gun at a fraction of the price of an unmessed H&H. Done wrong it would be an expensive money pit.