I had one shoot off once way back when I owned a barrel like that. You are right that this will have to be removed so that your FSB can be removed to allow installation of the YHM tube.
It looks like this underneath:
If you had access to an arbor press or hydraulic press, you could press it off by placing the barrel in the press, muzzle up, supported by the bottom (rear) portion of the faux FH. Then find or make a softener out of brass or hardwood so you don't damage the muzzle. Using the softener between the muzzle and press ram, press the barrel out of the fuax FH. Remember to catch your barrel so it doesn't fall onto the floor.
There are likely other WECSOGer methods of taking it off, like finding an open end wrench that fits over the barrel and makes contact with the bottom or rear of the faux FH (11/16" seems like it might work) and by hitting the open ended wrench, beat the faux FH off the barrel. Duct tape around the barrel would help to protect the barrel finish while doing this.