Cut the 16" down to the length you have listed and you are GTG. The 7" one is not permanent as you can change uppers. I have a 7" 22 upper. it's not the OAL i applied for, its also not the permanent 223 set up either.
YMMV.
I know this was discussed here before, where who knows?
The Great Kazoo's Feedback
"when you're happy you enjoy the melody but, when you're broken you understand the lyrics".