opmac and fonts

[Karl Berry]

Hi Gavin - FWIW, I recently re-discovered opmac.tex, written by Petr Olsak,
which has support for a number of the usual free font families. It stays
close to plain, so might be plausibly adaptable. I admit I haven't
looked at the code, though. Just thought I'd pass on.

It's distributed as part of Petr's csplain, but I believe is essentially
standalone functionality.
https://ctan.org/pkg/csplain

Best,
Karl