It's pretty easily done? Strip out everything but body, make a wrapper to include the pages? Any static bits you can search-replace, that's what I used to do before discovering server-side includes.
I am talking about 974 HTML files of which probably more than 95% is static content. Doing this manually, will take me about a year (considering the time I have available). So, maybe I should develop a script/parser to process the contents and generate them as server-side includes? But what is the benefit? That I can change the layout more easily, while first having to learn how to efficiently work with server-side includes? (Now I am just uploading my HTML files through FTP to my very cheap hosting provider.) But why would I? I am not interested in the layout, just the contents. I am not writing the website for a broad public, it is mainly because I like to record events (big and small) in my life. I guess, I myself am the most important user. Sometimes, I can surprise people by telling them the exact date that I did/experienced something.