Well, I am certain that you all probably know more about the different versions than I do, so I stand corrected.  Incidentally, I verified the serial number many years ago at a web sight that showed the history of springfields.  I also verified both of my Trapdoors at the same sight...  It sounds like that web site might not have been correct (hope my trapdoors are still ok).  Anyway, if anyone knows anything about that rear sight, I would love to know...  Ultimately, I am going to remove that sight and have a scope mounted so I can accurately sight the gun.  Thanks very much for the information!