I used pictures, framegrabbes, and movie reference for the stuff that is on the car. I'm pretty confident that my roof gizmos is acurate to the movie version.
I'm sure it is too 
but it looks plain and undetailed compared to the rest. Even if it's not in the original you shouold make some stuff up and make it more interesting. Look at the "gun" thing on top... it's just two cynlinders, add some knobs and twiddles etc etc. Believe me it will make all the difference.
Alan
Technical Director - Framestore
Currently working on: Your Highness
IMDB