Never seen them like that, every one that I have worked on had two screws holding that small reenforcement strap on. My guess is those are pressed in place, so I would try to wedge them out. If that fails, a Dremel cut off to remove the heads, then pull out with grips/slide hammer. For the future, and just my opinion, but I'd drill and tap for a SS 8-32 screw. The flappers are important.