I have two Marlin Guide Guns, neither have red dot sights but one wears a Leupold 2.5x Scout Scope.
Normal factory .45-70 Trapdoor friendly ammo kicks about like a 20 gauge. Levergun level ammo kicks like 2 3/4” 12 gauge. My favorite load is a 360gr cast flat point at 1,850fps. Recoil is like an exuberant 3” 12 gauge turkey load. Any Aimpoint and most other decent brands rds should live a long productive life on a .45-70 Marlin.
And yes the SBL is a sexy beast.