guess the people above arent helping you, I'll try my best.
GBBR external are mostly compatable with firearms with the exceptions on barrel, and inner assembly.
The barrel of GBBR is signifcantly different than aeg I suggest you search for something in the aeg field. all other external will work...if the rail/ mount as not different spec (some rail are molded badly and thus wont work with alot of accessories)
the grips and stock tube are something thats also not compatable. AEG have thicker grip, while GBBR is simply model after firearms ones. stock tube for the GBBR is for recoil spring on m4/m16 while AEG could be used to store battery.