I have been hooked on the silhouette game for several years and have several big bore lever rifles and pistol cartridge lever rifles. The Marble tang sight is a good choice as well as the Williams fool proof target knob sight. They both work well for the pistol cartridge course of fire.
I also have a Lee Shaver economy soule sight on a 38-55 Marlin CB. I shoot a 270gr cast bullet that leaves the barrel at only 1,030 fps. The front sight is a medium height Lyman 17A globe. There is 27 min of adjustment between the chicken and ram. The Lee Shaver sight provides the vertical adjustments needed with ease and repeatable accuracy. I have a 45-70 and 30-30 that both have the Williams fool proof target knob sight and both work well with the factory front sight or low 17A front globe.
For the pistol cartridge course of fire, there is no need for the Soule type sight. However, I understand the difference between need and want!
Look at (Bullaloarms.com) for a wide variety of the Williams fool proof target knob sights. I have the side mount version. They may also have a top mount version that attaches in the rear scope mount holes.