Here's a 9mm conversion that you don't have to have a different lower with the special 9mm mag well, you just use your 5.56 lower and of course you'll need a 9mm complete upper. I personally feel the mag well adaptor is overpriced and near the price where you can can purchase a dedicated 9mm lower. Enjoy the video.
https://www.youtube.com/watch?v=siavaA2mWms