[Ashus]

Hi.
You could try to compile it yourself. Checkout the git tag for the mentioned version (19.07.10), and set up the environment using official howto. Use my config file from ath79 as base (rename the file to .config), remove stuff related to ipv6 and add this package: luci-proto-ppp with its dependencies. Build it and if it succeeds, flash it.

We're a BSD house and have no Linux development systems. Could set one up, or pay someone to do it, but it'd be easier if someone had already done such a build. Do you know of anyone out there who might have done this?

Sorry, but I can't build it for everyone's special configuration. I use Windows, and compile this in a virtual machine (Debian). There are guides out there, probably even in this thread.