Existing GWT App - Mixing server/client models

We have an existing Single Page Application written in GWT. It has a top/header menu, and about 4 major subsections.

If we kept the top header/menu for all sections client-side, could we display the lower portion of the page from the server-side? vice-versa?
Is there a way for the server vs. client components to interact or try to design so they don’t?