I too am looking at doing a pinewood derby Viper.
Search on pinewood derby on the site to get some good tips.
There was a thread where I found some pictures of a Viper-ish looking model. I was going to use that as a base template.
Other Forum post
I'll get photos up of the car once may son and I are done. They have a category for pinewood derby car that most resembles a car. Hoping that if we don't win the race, we may win some prize. But I am shooting for a win. I have the balsa wood already for the front splitter and rear Aero. I also have a Gen IV 1/18 model ACR sitting on the desk we are using as a guide.