Czechmate,
It that a crack starting above the red arrow, at the junction of the "standing breech" and "water table" ? I didn't notice it in the smaller photos. If it is a crack, it will rule out returning the drilling to shooting condition. If it is cracked or welded, it will not pass proof. The welding at the firing pins would be removed in installation of "bushings", but it would be obvious at this location.
Mike