Your rifle is a model M1873 (the "8" is really a deeply stamped "3") It was assembled in the 4th quarter of 1884. As has been noted, this would be one of the last with this stamping, the subsequent M1884 is just a few thousand away. THe stock stamp is an inspectors Cartouche, with the intials of the inspecting officer assigned. In this case probably SWP, for Samuel W Porter.