This is a standard Mil-Spec upper receiver, so you will be dropping it into a standard Mil-Spec Lower. The EndoMag should function correctly, as the included BCG functions with Colt SMG and Glock magazines, just like the EndoMag is designed to do. Stern Defense also offers several variants of AR15 magazine adapters for different pistol magazines, as well.
https://www.opticsplanet.com/stern-defense-mag-ad9-ar-15-glock-9mm-40-magazine-conversion-adapter.html