"The rear sight appears to be a M1879 Carbine sight ( marked with a "C" on the side )."
Agreed. See Frasca/Hill p.84.
"The block is actually marke"d 1873"
You may well be right, but...
1) The last figure could be a 3" or an 8. Perhaps dttuner can clarify this? I thought it was an 8.
2) I am aware that there was no such thing as an "official" Model 1878. But, as the authors point out, there were numerous in-between versions.
On the page I cited the 4th breech block from the left appears to be marked US Model 1878. Maybe it's just my poor eyesight?
This version/edition/variation, call it what you like if you don't like the word Model - although that is what is stamped on it - has the rounded shoulder of the 1884 version. The versions clearly marked 1873 all have square shoulders.
3) In any case, the rifle appears to be a mixture. The stock appears to be made for a rifle with screw-clamp bands, hence the lack of band springs.
4) As the unfortunate object is way off being a "correct" collector's item, surely dttuner's first priority is to get it going as a shooter?