Well, *that’s* even easier ! Now I have the look-n-feel of the long defunct https://minimal.cx/ site
Just created the header and footer as two custom macros, then altered the main index page to call those in place of the existing header and footer ones. That way I could still go back if I made a real screw up, but is all appears to be good.
Most of the links will be dead, and only the index page has been changed into my format so the Archive et. al. will appear in the old (but not original) template.
Now I just need to add the older entries with suitably faked up dates to they fit the right format, and to get the date and time to become the header for each item rather than this method, and it’ll be hard to tell from a surfing POV that it’s a blog rather than the old hsc/BeOS static site 🙂