The problem with "AK-series" and "AR-series" firearms in Kalifornia is that they are subject to two "ASSault weapons" laws - Roberti-Roos and SB23. Roberti-Roos bans firearms based on the model number. However, the "series" designation was expanded after the HCI lawsuit was ruled on at the state supreme court as defining any similar model as a "series" firearm. For example, the Saiga sporter is considered an "AK-series" firearm, despite the absence of any evil features. Therefore, you would have to devise a new reciver to attach to an AR upper to circumvent the ban. SB23 bans firearms based on features (pistol grips, detachable magazine, flash suppressor, grenade launchers, etc.). Your time would be better spent taking the gas tube out of a FAL than trying to fool with anything related to the AR15.