Those are covers where the foam was injected beneath the floor. It was the only way they could do it and hide the holes.
You can take them off and put in a base for a pedestal seat.
I am sure there is aluminum under the floor also to attach screws through, or at least there is supposed to be so the seat boxes are attached all the way through the floorboard, and the aluminum. Also the screws do not align with any pedestal bases. You will most likely have to make the hole bigger also to accept the base.
Hope this helped.
Happy Fishn'

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