I have a 5.56x45 chambered Galil Ace that I need to get engraved before it becomes an SBR. Any idea how to do this. I removed the pistol grip screw and both the left and right selectors, but something's still holding it on. It looks like the lower would just rotate down from the receiver at its back and the front could be pulled out from the lower handguard, but the lower won't budge down at the rear. I can't see anything that's holding it in place. I've read about people removing them, but nobody has provided a how to. Any ideas?