Indeed there is the loose end of the 4 neutrons in Fe-56. Fe-56 is a perfect-cube of 3^3=27 where we have 26 protons as a unit cube chemically bonded to 26 neutrons much in the same way that bronze of copper and tin atoms are metallic crystal cubes. However, there are 30 neutrons and there are those 4 remaining neutrons.
So where do those 4 neutrons position themselves? Do you occupy the 27th unit cube? Are 4 neutrons able to bond to one another? Do 4 neutrons have some connections to the shell electrons? Do 4 neutrons form a sort of embryonic-alpha particle?