The transom and the bulkheads should be plumb. I am not sure about the various GRP types but in a woody the the top of the CB is lower near the mast then it is near the thwart, not even the floorboards and the benches are level. According to the official drawing of a woody, the floorboards slant slightly down towards the mast and the benches up (?!?). The benches are almost level though. The waterline in the official drawing, just touches the bottom of the keel at the transom.