IMHO you would have to go fixed-mag on the M1 carbine. Per CA definition, anything with under 16" of barrel is a pistol.
"12001. (a)(1) As used in this title, the terms "pistol," "revolver," and "firearm capable of being concealed upon the person" shall apply to and include any device designed to be used as a weapon, from which is expelled a projectile by the force of any explosion, or other form of combustion, and that has a barrel less than 16 inches in length. These terms also include any device that has a barrel 16 inches or more in length which is designed to be interchanged with a barrel less than 16 inches in length. "
also 12001.(f): Nothing shall prevent a device defined as a "handgun," "pistol," "revolver," or "firearm capable of being concealed upon the person" from also being found to be a short-barreled shotgun or a short-barreled rifle, as defined in Section 12020.
So it can be both a SBR/SBS AND a pistol.
If it is a pistol you run afoul of:
12276.1. (a) Notwithstanding Section 12276, "assault weapon" shall also mean any of the following:
(4) A semiautomatic pistol that has the capacity to accept a detachable magazine and any one of the following:
(A) A threaded barrel, capable of accepting a flash suppressor, forward handgrip, or silencer.
(B) A second handgrip.
(C) A shroud that is attached to, or partially or completely encircles, the barrel that allows the bearer to fire the weapon without burning his or her hand, except a slide that encloses the barrel. [M1: Yep]
(D) The capacity to accept a detachable magazine at some location outside of the pistol grip. [M1: Yep]
I just don't see any way around it.