More specifically on the Strike Eagle, the prototype was a modified B model, and it shared alot of airframe commonality with the Fighter Eagles. it did get differrent engines, radar and other avionics including the hardpoints for the LANTIRN system and later FLIR/targeting pods. it also carried the FAST conformal fuel tanks more regularly, although the C/D models could always use those and the Es have been spotted over the last couple years sans FAST tanks to act in an air to air dedicated role. finally, some inside structure and the landing gear was beefed up to handle more weight and down low flying (the original operational environ for hte Mud Hen)
The Super Hornet is more of an "inspired by" the legacy Hornet than an evolution.