The United States didn't really "outlaw" hidden headlamps . . . they just fell from favor as new technology allowed headlamps to assume sizes, shapes and configurations never possible with the old incandescent lights - which sometimes had to be hidden to conform to the stylists whims. That, and the added weight and complexity of the pop-up mechanisms finally did them in. They simply weren't necessary any more, as the headlamps could now be made part of the exterior styling of the front end no matter what the contours. Witness the C6 and now C7 Corvettes abandoning the feature, for example.
I wondered when someone would pick up on the "Zest II" appellation for the puzzle car. Sometimes the solution is pretty simple, but we don't see it. Another good puzzle.