godogz, as promised, here are some pics for Topper 158 scope mounting I have. No doubt there are other ways to mount a scope on a Topper, but if there's another scope base that won't require the rear sight to be removed, I don't know which it may be. And I like a low scope mounting (particularly with the straight stock I use) so my hammer extension is one done by Quickdtoo, drilling and tapping into the hammer spur to fit a Winchester screw-in hammer extension - I think it is a Winchester, if not, I'm sure Quick will be along to provide the correct info.

. (scroll down a bit for a better view of the hammer extension.)
Scope is Weaver K3, mounts Weaver detachable, base Weaver 60A.

Scope detached from the mount.

Top view of mount, note how it does not interfere with flip down rear sight.

Next two pics show side views of mount and relationship to rear sight.


The complete rig:
