I’ve already resolved the issue, but just in case someone else runs into this.
I did a full backup to ISO and installed it on a new device (to replace my existing IPFire device). When I finished configuring the new interfaces (only RED and GREEN on both) to match the new adapters after a reboot the DHCP server was not starting.
What was missing was the symbolic link in the rc3.d directory:
# ls -l /etc/rc.d/rc3.d/S30dhcp
lrwxrwxrwx 1 root root 14 Feb 15 22:40 /etc/rc.d/rc3.d/S30dhcp → …/init.d/dhcp
All of the others were present and after adding the link everything works correctly now.