I would recommend dedicated lower.
I would agree that a dedicated lower is best. As I recall not all hammers will work with the 9mm "bolt." I shoot PCC's (9mm AR-15's) regularly in matches and have for years. They're fun and cheap to shoot. In the last few years a lot of people have gone to the SIG's which are a gas design, not blowback. They have much less recoil than the blowback design with the very heavy bolt/carrier.
