Right now I'm too lazy to look up wether you have a free float tube or standard handgards and you didn't specify. If it's a standard handgard get the adapter made for AR handgards
by Harris. If it's a free float tube get the stud fitting where you will have to drill and tap a hole in the FF tube. Use red loctite to hold it in and use tweezers and hemostats to put on the nut between the FF tub and the barrel. Not an easy task but it can be done without removing the free float tube from the rifle.