If I put a rear casting deck in, I would design it like the modern boats do. It would require modifying your splash well. Make the SW smaller and centered, drop its height to the lowest point of the transom. Then build the deck around the SW and out as far as you want. See pic below and note that part of that deck are seats that fold down to increase the deck size. Flipped up, more seating. Its what I originally wanted to do to my boat. Google rear casting deck and let your imagination run wild
