Those fuel pump nuts are a nightmare and more if you do not have a tool that facilitates the disassembly and assembly, here in Venezuela is seen in many workshops that remove them turning them with a hammer and a chisel blunt but heat and time always crystallize the material and become brittle, I made with a plate cut into three parts bent in C in the center piece welded a quadrant of 1/2 "and the edges made sliding screws to graduate the diameter of the nut.