After a lot of reading and consideration, I chose 3/4" exterior grade 5 ply B-C sanded for the transom. I learned something as I was taking this boat apart. Whoever added on the front deck , did an excellent job. It was glassed on the underside as well. As I was ripping it out, I noted that they had seriously scuffed the surface of the plywood prior to laying up the glass. It only makes sense. So, after tracing the pattern from the old transom, I scuffed it royal. With a 34 grit flapper wheel. Wiped both sides with acetone, and laminated the 2 pieces together with chopped mat. Clamped it, let it set, and that is what you see.