Piece of 1/2" (12mm) or 3/4 (20mm) steel pipe.
Cut a slot in the end big enough to go over the wings.
Hole in the other end, use it like a box spanner.
It'll probably turn the flats off the bolt, then just use a hacksaw blade as above...

Buy a close coupled seal kit as well.
You get new seal, bolts wing nuts and plate.
.