'Imnotwithreal' - The Scope is a Weaver K-3 from the 1960's. It is 3 power
and has a 1 inch tube.

The Filler Blank is probably held in the barrel Dovetail by fit and friction. It can probably be driven out to the right with a brass punch and plastic mallet.

If you have a old time Gunsmith around,  he would knock the blank out and  install a leaf sight while you wait for a modest price. (But, I may be delusional)!