Given what you say for your anticipated ranges,
Giventhe riflesyou already have,
Given your apparent preference for non-magnum type cartridge selection,
Given the concept of cartridge spacing (and then some)....

I'd go with a 45-70 in a Marlin lever gun, quite possibly the "guide" version,
Sites? Experiment in your own "at dusk" conditions and decide what you want, day glow irons, peeps, heads up red dot, or low power variable illuminated reticle scope (like a Lupy VX or Vari X III in 1.5 to 5). The latter would likely be my choice.