This is my understanding after speaking to my local DA, a local Judge who convicted someone of a concealed rifle in a truck, at local lawyer and my local LEO. In order to be charged for having a concealed long gun in the cab of a truck, SUV, station wagon, jeep etc... the it first must be concealed and secondly it must be accessible. It doe not have to be loaded. It is my understanding that ammo also has to be accessible. Loose rounds or boxed rounds are less accessible than say a load magazine. The accessible part is where the rubber meets the road.
If you are pulled over with a long gun in the car and the officer discovers it they will make a determination if the gun is concealed and accessible. The NC statute is not explicit as to the definition of accessible. I was at a dinner party with a local judge and a lawyer who is also a member of the NC House and they were discussing a case where the Judge convicted a woman of a concealed rifle in a truck. The lawyer was the defense lawyer in the case. The gun was in a soft padded case with loaded magazines on the floor board of the truck behind the passengers seat. The lawyer argued it was not accessible. The judge said it was. The women was convicted.
So I asked what in that situation would make the gun inaccessible. I was told that a simple luggage lock would have changed the determination in that case. I also later asked local LEO and my local DA about the same type of scenario. I was told that in my local jurisdiction it would be unlikely for me to be charged if the gun was not loaded and it was clear I was headed to the range. They advised not to have any loaded magazines. Both agreed that a simple lock would put you in a stronger position if you were charged and brought to court. They also advised depending were you were traveling within the state some LEO will interpret the statute differently.
My issue with the statute is that you are at the mercy of a individual LEOs judgement and then most likely the judgement of a local DA and Judge. Lots of wiggle room for too many people. I generally only transport long guns in the trunk of a car or with a lock on the case inside my truck. YMMV
Yes make sure your FFL transfers as other. It does not matter if it has a stock, carbine tube, grip etc... It is other until you attach an upper to it. It is my understanding that once you place a rifle upper and a stock onto the lower it is then a rifle forever and cannot be turned back into a pistol. A pistol however can be converted into a rifle and then turned back into a pistol.
I went with 11.5" because of reliability and because of sound and muzzle blast. I found it to be a more enjoyable shooter but my understanding is that 10.5" is the shortest one can go and get rock solid reliability. That is not to say people don't have shorter guns that run 100% just that at 10.5" and above the odds are in your favor. If you are looking for a SBA3 Brace I have one for sale. It is brand new in the box. I mounted it but did not shoot with it. I ended up going with a SBA4. Shoot me a PM if you are interested. With all the craziness these days they are out of stock in a lot of places.