The flathead allen screws can be very tight. I broke the head off one. Penetrating oil and some gentle heat would be in order. There are two screws and two dowels. I did not try to remove the dowels from the barrel since I was only interested in taking a few thousandths off the back end of the rib.
IIRC I was able to unscrew the broken stub with vise grips after the second screw and rib were removed. Ruger sent me a new screw.
