Harrington and Richardson (not H&R1871) built the Officer's Model as 'their' Centennial commemorative - providing an optional oval brass plaque for installation.
The big difference between that and the original Model 1875 is the fact that H&R provided a tang sight only, whereas the originals all feature the current-issue Rifle sight and base.
An original sight will neatly fit the barrel's contour, needing only to be drilled and tapped for installation, should one so desire.
The drawback (if any) is that the bottom of the rear sight's base will obscure the very top of the Harrington and Richardson lettering on the sides of the barrel - but installation of an original rear Rifle sight gives more sighting options and completes the 'look' of the piece - as would the addition of a Beach front sight.
Many of the parts are original, since it was easier to buy and refurbish things like barrel bands, buttplates, triggerguards and such, than it would've been to create from whole cloth - and they bought many Trapdoor parts from S&S Firearms 'way back when'.
They built the popular and engraved 'Little Big Horn Commemorative' (provided with the book - 'The Seventh and the Sioux') as well as the 'standard' carbine and rifle with leaf sights.
As has been mentioned, there was some trouble with the cam latch - but I've never encountered it, and I use factory smokeless only.
Vaya,
Scouts Out!