Can anyone please provide info how to build Replicant 6? The documentation seems outdated (I have reported that in the tracker).
You are correct in stating on the tracker that Debian 9 is an old distro. When I built a custom version of Replicant 6 a while back, I downloaded the iso for Debian 9 and built it in a chroot. I know this doesn't completely solve the issues but that approach worked at the time for me. Possibly if you know how to script you can modify the following to work for 'generic' Replicant 6.0 instead, alternatively you could script your own way of doing the equivalent.