Just occured to me that you might need to be careful using another boat as a patern. They might not be the same. Try to find one with a number close to Fairey Mary to minimise the risk of there being differences.
Also you might want to think about a Bimini. Not as easy to do on an Atalanta as on a Titania because you have a bigger cockpit. The main problem will be keeping it low enough to clear the boom. I raised the boom on my boat (to reduce the risk to children, who are now adults), but it does make it easier to add the Bimini.