The hole's too big, and if you'll take the trouble to drive out it's cross/retaining pin, and remove the safety, you'll see the the safety detents extend beyond the sides of the safety shaft hole proper - the reason a replacement plug should have a flange on the top end to sover the divots.
The plugs, whether you make one or buy one from www.stevesgunz.com are held securely in place by that crosspin - accessible through the locking lug grooves when the bolt is open.
I used a toothpick & some laq thinner to remove the red/green paint from inside the stamped "S" & "F", around the old safety hole, making them fairly hard to see.
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