On the little screws. I would use map gas to heat it and PB Blaster penetrating oil. Heat it, spray it, attempt to turn, repeat. It may take an hour test of patience. If it is still being stubborn I will use the hammer type impact. Again patience. The screws are small enough to break by hand. If you can get it to move at all you should be able to remove it with heat and PB.

BTW I would use red loctite on the screws when assembling.