20in AR upper free float upgrade

I am wanting to buy a 20in upper with a free float handguard. The upper I have been waiting for from BCM (http://www.bravocompanyusa.com/BCM-20-Rifle-Upper-Receiver-MI-p/bcm-urg-std 20 mi ss15.htm) has been out of stock forever. PSA just put up a 20in upper(http://palmettostatearmory.com/inde...ped-upper-without-bcg-or-charging-handle.html) that is in stock at the moment. My question is what would I need to add a free float. I know i need a low pro gas block with correct gas port size and obviously the handguard. I want the MI SS15g2. Also what is the difficulty. I have never done a free float just standard. Thanks in advance.