I found this blueprint of the car.
Very nice looking car.
As others have said, it would be a shame to mess up the look of the car.
I would do the same as others have mentioned and block the grille down to the very bottom slat that you can leave open.
If you take your time and put some effort into it, you can do a grille block that won't even be noticed to the casual observer. Personally, I would have the grille block behind the grille mesh and
painted flat black so it will be stealth.
A few here have done some really nice blocks that look totally factory :
http://ecomodder.com/forum/showthrea...eza-30402.html
Lower the car and this will not only improve the drag, but the handling and looks of the car.
The rear of the car is very rounded and this is a problem as the wind separates and causes a lot of turbulence. There is not much you can do that wouldn't mess with the look of the car and the function of the spoiler, but you can create some professional looking trip strips that wouldn't mess up the look too much.
The open spoke wheels could be replaced with smooth wheels when you race, and a full underbelly pan would be invisible unless you flipped the car :-)