I am fascinated with the idea of a .410 bore Trapdoor.  Looks like a lot of fun.  Were it mine, I would not be in a hurry to restore it.  Is it really a .410 or simply a .45-70 that someone shot .410 shells in?  There is no reason that you can't put a shot load into a .45-70 case and use it as a ".410 equivalent".  Where did I put that hand thrower gizmo?