Beautiful work my man. I don't know if it's art but I like it. I understand what your saying about the shape was pretty much chosen for you but if you can fit a NACA style duct in there that would probably work a little better at the top end. NACA ducts are a proven design that allows the movement of air from outside the car to the inside or vise versa with the absolute minimum amount of drag and air turbulence.
Brief overview of NACA ducts:
http://www.yft.org/tex_vfr/tech/naca.htm Plus there are some neato racing supply web sites where you can buy them pre-made.
http://www.kenlowe.com.au/raceglass1.htm http://www.ioportracing.com/bumperduct.htm Not so much a car page but it has a great pic of a duct. Apparently there are more then one kind of NACA duct although people tend to think of this style.
http://www.wisil.recumbents.com/wisil/nacaduct/naca-duct.htm After all, that 143mph drag limit is, well, a drag
