I have one that i converted using a 9mm conversion kit that i bought from J&T distributing a few years ago. I think thats their name. But anyways, it came with the whole upper receiver kit including the bolt carrier, 9mm buffer, and mag block. total was about $700 something if i remember correctly. Its probably cheaper now.
I didnt need a new tirgger hammer or anything bc the guy said mine would work fine. Im not sure if u were to need one based on what type of lower you have. I had a rock river arms complete lower receiver.
The mag block I have clips into the lower like a magazine would, then you have to tighten this allen screw to hold it in place. I also recommend using the colt magazines if you can afford them. theyre pretty high in price. I havent yet had any problems feeding with it, my other mags suck. If anyone can knows of a cheaper one that performs as good, id really like to know. thanks good luck to ya man