If you go here:
http://shelbycsxinfo.com/3000-Series/
you'll see that several cars have diagonal orientations of the lenses and that same gasket gap you are referring to. However, given that you are bent on being original, the vertical face of the mounting area is not 90* to the ground as is suggested by your side view. The area where the lamps mount is slanted to the rear at the bottom, like this:
The incorrect body details like this are far more noticeable than the lamp orientation.