Boomfab is correct, it is indeed carbon fiber reinforced Nylon66. If you're doing a conversion, you'll probably have enough scrap for the welding.
Devcon Platic Welder II works well because it's a "reactive" adhesive in that it creates a "chemical" bond... almost a "fusing" behavior. Additionally, it's designed for tougher to bond materials such as Nylon 66.
In the end, I prefer a "welded" approach... it's just a matter of getting your weld deep enough with enough heat to not only melt the weld rod, but enough of the surrounding material to get a good weld. For anyone who has done welding with a mig-welder, you know very well that the weld goes deep and and is reasonably wide.
I just got done welding in the "window" cover and gave it a good "whack" with a mallet... good to go. I also let the bolt carrier freely slam a dozen times or so... all is good. Ultimately with the back end, time will tell as it will take more of a beating than the window cover. I'll keep you guys posted.