A. It is a hinged stock design that folds from the back of the gun's receiver on both the original M3, the unauthorized redraw (which one could argue doesn't even factor in since its not part of SARP), this design is also used on the Bushmaster ACR, FN SCAR, CZ-805, at this point hinging the folding stock on the end of the receiver seems to be general practice in the real world. However the SBR's receiver extends outward slightly before hinging unlike the M3 and other designs and also has an extending capability we do not see in the M3 or it's redraw.
B. Rostov and Kriegler already have an AR-15 pattern rifle in production and if you would look closer at the final pattern you will notice there is no magazine release on the right side of the weapon, it is intended for the user to grasp the larger 7.62x51mm magazines with their left hands and press the drop free AR style release with their thumb. This was a personal preference over AK style tab releases.
C. The SBR employs an AK style charging handle directly attached the bolt, simple, hard to break, easy to use, much like the actual SG550 (which is a westernized copy of the AK pattern). The M3 seems to employ a top mounted G36 style charging handle set in something akin to the SCAR's forward charging handle.
D. Its roughly similiar in shape, then again so are several other rifles however where yours stops at the hinge point of the stock mine continues, same with the forward area ahead of the bolt.
E. Mines a dial style system with similiar structure to the FN-SCAR, yours is something directly taken from the SiG SG rifle.
F. See above (although one could argue the M3's standard art makes it hard to determine).
G. The actually does have a right side ejection port, that image is reversed and there for the sake of showing shape and scale.
H. I'm assuming the canon art is a direct copy of the 552 Commando's handguard which means its not even close to what the SBR employs.
http://www.thespecialistsltd.com/files/Replica_SIG_552_Swat.jpg
In the end there are a few things to consider, one the redraw while similar to the standard M3 art is a unique piece one which I made and which you chose not to use, as a result anything that is not directly related to the M3 (the stock, the handguard, the barrel, the pistol grip) are mine to use on other systems as I see fit because they barely match the M3 any closer then any other rifle in real life. One could also note due to the basic style of the M3's art (the lack of many details beyond basic shape) it fits and looks like a wide variety of possibilities if one looks hard enough.
Edit: As an additional note I'm going to add a change of location for said corporation to an unincorporated colony somewhere (possibly in Yugumo)