Circa 1876 Trap-door Rifle questions?

[butlersrangers]

I saw a U.S. Model 1873 Springfield rifle at my local gun shop yesterday. It was in the 68,6XX serial number range. The lock-plate was marked '1873', but the tumbler had three 'cocked' positions. The breech-block was 'high arched' and the action fit the stock properly. The rear-sight was a model 1879 type, held on with slotted screws. It had a model 1878 style clearing-rod. The Stock 'cartouche' date was illegible. The overall condition was Very Good.

Is this a credible combination of parts? Were earlier high-arch Rifles updated?

Does an 1876 vintage Rifle bring a premium?

[Dick Hosmer]

(1) Good description!
(2A) Yes, was originally 3-notch by then; block change from high arch to low (but still narrow!) and lockplate from date to no date, are both "fuzzy" - no firm date on either.
(2B) Not normally, other than rear sights.
(3) Only if completely original, included stepped sight with slotless screws, and in the higher grades (visible cartouche, etc.) and then only slightly so.

[butlersrangers]

Thanks Dick for the quick and concise reply!