No offense, but I don't think you will get a lot of free troubleshooting with installing an old, obsolete release for a problem which is only theoretical in your case.
You can even take the "in your case" part out, where ever that info is coming from is wrong - QoS hasn't changed since before 1.2.1 release, same config code in 1.2.2 and 1.2.3, no diff aside from the minor FreeBSD version change which didn't change things related to that.
To install on something with less than 2 NICs, just type "exit" at the prompt to assign LAN.