I'm law enforcement.
However, in this "formation," it's 100% legal for any California citizen (who is legally able to purchase a rifle) to own and build.
http://www.calguns.net/ -- read the FAQ, read PC 12276 and PC 12276.1, learn the law through and through -- and do it yourself.
Realize, you are right
on line regarding the LETTER OF THE LAW... so be sure you understand those two penal codes, as well as the FAQ, 100% before you build one -- otherwise you could get yourself in serious trouble (by building an "assault rifle" by accident, that's a felony).
The SPIRIT OF THE LAW is to remove all weapons like this, and similar ones from California; However, SPIRIT OF THE LAW is not the LAW... the letter of the law is.
Anyway, read, and if you have questions... ask there. If you aren't sure or are uncomfortable/confused, don't do it.