Superman debuted in Action Comics #1 of June, 1938, so he turns 70 this year. This is a homage to the cover of that issue. Superman's torso is the only customized piece here.
The biggest headache with this wasn't finding all the green pieces to build the Studebaker (although that was quite a pain). Nor was it finding the right facial expressions on the minifigs. It's the fact that minifigs can't raise their hands above their heads, so Superman doesn't quite have the classic pose. Sigh.