Try the black powder forum on here, you'll be targeting more of a specialty group & that may help you get info.
The 2 triggers are probably what is called a "double-set trigger" the front one is the "real" trigger, & the rear one is used to "set" it (give an extremely light pull)
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”