XS Sights or whatever they are called these days made a rear aperture "ghost ring" sight that would mount in place of the rear scope base - probably using the factory drilled and tapped scope base holes. NOTE: I have XS Sight #22-2015A-058-1 which uses two mounting holes 0.605" centre to centre - I have not yet found a factory rifle with that hole spacing for a rear scope base. There is at least one maker who makes a rear aperture sight that clamps onto a Weaver style rear scope base - I do not readily remember the maker's name. Alternatively, Lyman makes a #57 SME Aperture sight - you drill and tap two holes on right sight - ahead of the bolt - fasten the base to the rifle, then the cross arm comes over top of rear bridge and is adjustable for windage and elevation on that base unit.
A most rudimentary one can be made and installed - look up how Finn Aargaard had a "L" shaped metal strap installed on his first Win 70 in 375 H&H - worked fine, as per him. No clue how they established the precise height to drill the aperture hole, but from pictures, there is only one hole there. Picture of Aargaard's rifle stolen from Internet:
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If you really wanted to get super funky crazy and also replace the front sight, this is a Parker Hale PH5B 2 as they used on their 1200 TX 7.62 NATO rifles - it includes a bracket that attaches to the two scope base mount holes on the rear bridge. This Parker Hale rifle is using a very similar commercial Mauser 98 pattern action as is on your Zastava - might even have been made at the same factory, some years apart. I understand that the identical rear sight and bracket was supplied by Parker Hale on the Canadian C3 sniper rifles - the guys carried the front and rear aperture sights, with them, in their Kahles scope carry box.
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