I also have a couple of disassembled 30P-mags ready to go. They're legal to keep in that state in CA.
You cannot put a 30 rounder (legally grandfathered or otherwise) in any BB AR rifle. That means you're creating an assault weapon (whatever the hell that means).
IMO, if you have an FAL/AK, go featureless. A muzzle brake/comp is kosher, only flash hiders are haram.