This an older post but I am going to have to respectfully disagree with the statement that these frame mounted safeties were factory installed during production. In most cases, the safety instal is well done and that tends to perpetuate the myth that it is original to the pistol.
The military M57 pistols only had the half cock safety. The frame mounted safeties were added before import (to US markets only) to satisfy BATF regulations.
As can be seen in the photos of the pistol in the OP's posts, the metal around the hole in the frame on the right hand side is not blued. Obviously where the hole was chamfered after drilling the hole. In most of them, you will also see the notch that is cut into the slide for the safety is also in the white (although not on the OP's pistol)
Some commercial made M57 "type" pistols made by Zastava have a
slide mounted safety but these are few and far between and most were in 9mm.
If you look at pictures and diagrams in the Yugoslav issue manual, there is no safety pictured or listed in the parts breakdown.
Lastly, on most of the M57 pistols, most of the individual parts have a 6 digit number separated by dashes. This is the part number assigned to the various parts. The added safety lever has no such number as it was never an official, issued part.
Picture of original, non import marked, matching numbered bringback M57 (notice the lack of added frame mounted safety)
