[jack404]

Cant help with the lever action but the tang mounts looks like a sure-sight mount

it was a after market tang mounted rear sight or vernier site

the front pillar fits the forward part and you screwed a knurled knob to lock it on it guarenteed to be able to hold zero for many mounting and removals

i copied my tang sight from one of these a long time ago but i did not do the propriety mounting , these came out just before WW1 as far as i know , i dont know the nation or origin, i think its US and i know theres a patent doc for the US ( as thats what i copied ) but as to the exact one , i aint got a clue , sorry, memory aint what it used to be