It appears that the upper receiver is a replacement, with no date, markings of notch cut out for the rear sight. I'm also a bit concerned with the toggle not closing completely in the photos, leaving a slight misfit along the front of the frame.
Here is a link to an artillery model for comparison to help you understand what I am referring to:
http://www.gunbroker.com/Auction/Vie...Item=531207006
You have a very nice gun, but we need to look harder at it to understand its past.
dju