T/C did make a White Mountain Carbine Flintlock. As I write this, I am looking at a picture of it in T/C Catalog #19. It is .50 caliber, octagon to round barrel, and 1 in 20" twist. I would guess that a T/C Hawken/Renegade/ Penn. Hunter, flint, lock would fit the stock. I also suspect that a T/C Flint breach plug (15/16") would fit in place of your percussion breach plug. Why not call T/C and talk to customer service, and the repair shop. they are very helpful. 603-332-2333.