Not much experience with ar9's although I have a 6951.
Have a spare forged SBR'ed lower. Plan to purchase H&R635 style upper. Mean arms mags with the ejector. Lower has a standard (not A5) receiver extension, which I will run an a5 buffer for 9mm for the extra length and also an ALG trigger.
Am I on the right path, any compatibility issues or things I should look out for?