I just acquired an old J. Stevens model 94b 12ga shotgun. It is missing the firing pin. Also, there is a threaded hole (1/4")in the breech face, where the firing pin would pass. Is there a part that threads in there, which has a hole for the firing pin to pass? Looking at parts lists and diagrams, I don't see a part. And I can't seem to find a picture that shows a view of the breech face. Anybody know about this?