TINKER ,on the stuck screw, try takeing the screw driver that fits the screw properly, and place it in the screw slot, while holding a piece of dry ice against the screwdirver blade. This will transfere the cold into the tiny screw, cauesing it to shrink. Then very quickly after the Dry ice is removed turn the screw. It should turn out fairly easily! When you re-install the screw in the new sight, put a little soft lock-tite in the threads in case you have to remove it again.
Another suggestion I'd like to make is, when you get the sight made to the proper hight, make another one as a spare so you have a replacement so if the rifle is dropped breaking, or bending you front sight. The spare doesn't have to be pritty, only the proper hight.

........Good shooting