RDB bolt is just regular 556 bolts with slanted cuts at the locking surfaces. The barrel extension is the regular 556 extension with a single 9mm feeding ramp cut into it. What kind of lower do you want to use? As long as you have a regular AR15 lower (with ARC mag) or a dedicated CMMG lower for pistol mags it will work
I believe CMMG sells the RDB barrel and BCG as a set. I also think (please do check with them) that their BCG can accept other bolts to make the action non blow back.