For ghost rings, I prefer to use ones made by Skinner. They come as a receiver mount, or replacing the rear blade in the dovetail slot. There's nothing wring with XS sights either. They're just a bit blockier than I prefer.

XS also makes a rail for a Marlin 1895 (round barrel only), which fits between the rear sight dovetail and the receiver, using two of the four threaded holes. I mounted a Leupold "Scout Scope" on the rail, which has a 10" eye clearance. This eliminates the need for a hammer extension, as well as the unpleasant meeting of eye and scope under heavy recoil of the .45-70.

Scout scopes run 2-1/2x to 4x, which is appropriate for the 125 yard or so effective range of the .45-70. You can shoot (much) further, but only with heavy elevation compensation. The drop at 150 yards is about 18".