Allan
According to Wikipedia the Arrogant class was based upon the Bellona design with similar dimensions. I have compared the Stemson, Keel, False Keel, Stern Post, Inner Post, Stem Post and Apron dimensions in your Arrogant class contract, the 1770 Culloden contract and the Bombay Castle contract. They are "reasonably" similar dimensions.
I have a high resolution profile for the proposed Bellona / Dragon construction. It has some stern/keel/stem details. I have taken measurements of the details listed above and find many are the same. The stern post and the stem post differ by as much as 6 inches.
I also have a high resolution draught for the Bellona et. al. I can see the stern post and the stem post in addition to the associated rabbit.
At this point I am leaning to a keel layout using the Bellona draught for the "visible" dimensions of the stern post and the stem post. I think I can add to that the dimensions on the other drawing.