'pjohn':
A good basic book on 'Trapdoor' Springfields is: "The .45-70 Springfield", by Joe Poyer and Craig Riesch (North Cape Publications - Paperback - about $20). It will answer many questions.
I believe your rifle, #320,08X, was made around 1886. It has the model 1884 'Buffington' rear sight. It has a 'Rod-Bayonet'.
At first I thought your Springfield was a Model 1888 - Rod Bayonet rifle, but, they did not start making those until the 1890s and they normally have a 'one-piece' trigger-guard. There was an earlier model 1884 (experimental) Rod Bayonet rifle of which 1,000 were built in 1885 and 1886. Possibly, your rifle is one of these, that was later updated and re-issued?
I would suggest that you post clearer detailed pictures on the 'Trapdoor' forums on "Culver's Shooting Pages" or the "Gunboards Forums" with your questions. There are some more advanced Trapdoor Authorities that participate there.
BTW - Nice looking Trapdoor!