Something that you may want to think about before you install the plywood. Depending on the thichness of the transom cap. Cut the camber into the top edge of the plywood and make it say 1/2in or 3/4in shy of the top of your existing transom top glass.
This will give you a ledge for the top cap to sit on and conform easier. I used 3/4in Kledgecell for my top cap. I laid it in a mold and glassed the bottom side. As I found out the mold wasn't really nessissary. It will conform with glass on just one side.
Seacraft's have a little more camber in the transom cap than I like. On an 8ft beam boat. The transom will a little narrower. I like the center 1 1/2in higher than the sides. This allows an easy surface to walk on and if your going to install any kind of hatch's it will be a little easier to make them conform.
http://www.classicmako.com/projects/xshark/bw4.htm