Then look like fuel baffles, in the fuel bowl........do you think you are dealing with fuel slash?.
I know you said it would launch just fine. but you said something about leaning idle mixture screw and a.......rough idle when stopping or something like that.
Just wondering if you might want to keep them. One of your carbs may not have had them installed from the factory...............
don't think this would have anything to do with you cruising/tip in stumble.