That woudl most likely be 1884, not 1864.
By initial observation it appears to be a cut-down rifle though without detailed photos it is hard to say.
There are immediate indications of a cut-down rifle;
-The contour of the stock nose ahead of the barrel band is too short to be a carbine stock.
-The Buffington rear sight and what appears to be the notched barrel band may be correct depending on serial number. There will be a letter on the sight in the upper corner of the flat leaf...will most likely be an "R"
-The trigger guard is from a rifle, the small loop on the front of the bow is for the lower sling swivel.
-The trigger is the correct late era grooved and checkered trigger.
The cam latch lever attachment is also correct being the peened over cam latch shaft....earlier models had ground flat cam latch shaft.
All indication say this is at least an 1880 to 1890 era trapdoor...all depending on the serial number.
Cheers
-The hammer is correct later period Post 1880, I can be the hammer nose projection on the bottom of the nose...this was introduced around 1880