I've been experimenting with Griffin Armament gated QD MDs.
Specifically, I have a 30cal flashcomp that I've been experimenting with.
https://www.griffinarmament.com/30sd-suppressor-mounts/Now, granted I have mine on a 5.56 barrel with a (shoulderless) thread adapter, but that's beside the point; I have confirmed that the length of the barrel with their 30cal MDs (gated QD ones, as linked) is still >16in.
A good estimate for added length of a MD is take the OAL of the device and subtract 0.625in. Hence, my flashcomp adds 2.15in for a total barrel length of about 16.3in once I get it pinned.
I will also be testing to see if their shorter 5.56 gated QD MDs will still work with a spacer and shoulder ring, but that won't apply to your case. Can post more info on that if someone else is interested though.
As for 922(r), that Reddit post is rather dubious in how it handles the assumption of the operating rod. Being that the charging handle connects to a piece which in turn *operates* the bolt, I'd still consider it until I see something saying otherwise. Again, for me its a non issue since I'm in 5.56, and can swap mags.
Since you're remaking the barrel, and now the muzzle device doesn't apply, I can still see a route to a count of 10 imported parts total if you also replace the trigger and disconnector with the HBI parts as well, unless you're running a CZ made stock.
Assuming worst (or best, if you have your hands on one, you lucky mf'r lol) and the op rod does count AND you do have the CZ stock holding you back at 11 parts: The mags are very similar to pmag ak mags though. Maybe swap followers or baseplates?
Side note, do get the HBI trigger and disconnector.
A. Becasue the trigger improvement is spectacular - all overtravel on both ends of the pull is gone as is most of the wiggle.
B. Because the disconnector is a cheap and easy upgrade if you're already pulling the trigger and one less part to worry about.