[PbFut]

The flanges are threaded onto the rod but could also be rusted to the tank bottom. The only way to get them off is to push the rod out. Maybe flange is rusted to bottom. Possibly grind the flange to expose the rod to work up and down to break free. It was a challenge to get the rods out on my tank and it appeared in slightly better shape than yours. The rod will be badly corroded and dirt works its way into the tube as well so there is a lot of stuff in the tube to work free.
One last important note. Fuel tanks can hold explosive vapors. Make sure you clean tank so as not to blow yourself up. If you can smell gas in the tank you are at risk.