I replaced the same ones on my Flats Skiff. If originaly they were secured with 5200 or the like, beware as they will crack & break trying to remove them. Try high pressure air or water to flush the debris out (Deck side as to keep the ball within from sealing the drain shut)
Make Sense?
The top piece should come off but be cautious see this info:
http://www.thmarine.com/products/Aer...-Scupper-Drain