I know this is sort of a matter of terminology, but the tang screw on a Lefever does not turn it into a manual safety. What it does is turn it into a Non-Safety. A little tenon on the end of the screw enters a hole in the safety slide when it is turned down, thus locking the safety in the rear Fire position. The safety is not meant to be moved as long as that screw is turned down locking the safety. What has happened to a lot of them over the years is someone who didn't understand them has Forcefully pushed the safety forward to the safe position without backing up the screw & breaking off the tenon in the process. They then of course no longer work as intended.
