Hey Jet, I'm in the same boat with the transom. (Pun intended) Incase you didn't see it, there is a thread I started titled "PICS" last week and Reel gave some very good advice for re-attaching the cap. As for a transom core, I'm thinking I'll use the Coosa board instead of Marine Plywood. Some of those guys on the classic maco site have sworn by it and I've talked to a few others who recommend it. It's a bit pricey though. I think it runs (on average) between 150 - 180 bucks for a 4'x8' sheet. It's suppose to bit lighter and stronger than plywood as well as bonding better and wont rot! But I can't swear by it because I haven't used it (yet). When I do I'll post pics! Good luck with your project 8)