Or use a script to pull your WordPress content from the database + republish on your HTML site.
Another trick.
Use some sort of markup language, like Markdown or AsciiDoc for your WordPress posts, so when you pull them from the database you can run them through an HTML processor to produce similar looking content on your HTML site.
Note: If you’re running both sites, first site index wins as the canonical link.
Second site will have a duplicate content penalty for each page + since this penalty will apply to all pages, this will promote/escalate to a site duplicate content penalty + likely your second site will be dropped from the index.
If you’re trying to SEO both sites, keep in mind, if GoogleBot is visiting both sites, which ever site is visited first wins.
This becomes ugly + complex if you’re trying to SEO the first site.
Likely best to completely block (iptables block of entire GoogleBot IP range) any indexing of second site… if you’re trying to SEO the first site.