Better to start the right way than have to repair a mucked up attempt.
If I was the smith I would charge more to repair one that had been glued and failed.
If it is still in proof and otherwise sound the value would go up a bit but you would need to find a Black Powder shooter to buy it. are determined by the condition of the gun, the amount of original finish remaining on the metal and wood as well as the mechanical condition.
It would have little value to much of the US, but much greater value to hammergun lovers - the best marketplace for it (a Vintager's Shotgun Fest, for example ), as long as the buttstock is unmolested.. Also the construction of the gun (i.e/ damascus barrels) are a factor. I think maybe the barrels are damascus and have been blued.
You might be better off and cheaper taking it to a smith to have it done properly the first time.