I don't believe there is a "standard" 9mm lower. But to answer your question, the PSA uppers will "fit" a standard AR style lower. I guess it would depend on which lower you pin your PSA upper to whether it will work or not.
AR9s are similar to the AR308s (AR10) platform with respect ensuring each part used is compatible with all others in the build. This is a completely different concept than an AR-15 style rifle. The reason is because the AR-15 has a Mil-Spec and the parts made to fit Mil-Spec are all completely interchangeable.
Thanks. I have an Ar-15 lower with the midway mag block. It's colt pattern. Just looking for a working, but inexpensive carbine upper to use in uspsa pcc class.