If you want relatively (ish) accurate drawings of the cars you could use the dimensions such as the track, wheelbase height etc given on Ferrari's website or if not get hold of the pictures of the F2003GA off of Ferrari's Website:
http://www.ferrari.com/cgi-bin/fworld.d ... ar_type=F1
(I was gonna give you the stats for the F2004 from this site but they seem to have removed the link for it.)
Then using these known dimensions scale and estimate other dimensions from the photos they have.
The dimensions (mm) of the F2003 GA are:
Wheelbase: 3050
Total Length: 4545
Total Width: 1796
Total Height (I assume this includes the hoop mounted camera): 959
Fron Track: 1470
Rear Track: 1405
You can find out the wheel diameter/width somewhere very easily too...
Excellent pics of the car are given in Paragon Press's Formula 1 Yearbook (ISBN 0-75259-146-0) my annual Bible of F1 info!
Hope this is of some help!