I have played with HAM conversion myself[0], but my approach has been to deliberately avoid brute-force. That's not just because it'd be less fun, but also as I'd like to get these algorithms working on the Amiga itself at some point.

My current local code has new strategies and also does dynamic hires, but it's an uncommitted mess.

0. https://github.com/rvalles/amigagfxmangle