Center section removal

I've used driving wedges. Thin, fine tapered, and sharp. Get some cheapy stiff gasket scrapers like Performance Tool and cut the handles off, leave a stub to hammer with. Carefully, very carefully, drive a wedge in just a bit. Keep working around, carefully deeper, and slowly, not gouging any metal. Eventually things will work loose. Once there's an area of seperation, you're on your way but not out of the woods. The key is patience, and to work around the flange and eventually it will work loose and come apart.