Seeing that your post was from 2001, and I don't know if you have ascertained the information that you were seeking, I'll go ahead and respond. The ZO7 code was introduced in 1991 when it was introduced with the adjustable suspension. What Set it apart was the stiffer springs, thicker sway bars, and I understand that the wheels are the same deminsions at all corners; 17x9.5. I have a 1994, so that is the set up on my car. The ZO7 cars were built to go racing, and GM wanted those with a Pro Solo License to obtain these cars so they would be used appropriatly. I don't know if many of them were used in the specific races, but Im glad that I lucked up and found one, as they are responsive cars. I did forget to mention that the ZO7 cars also have a quicker ratio steering box.
Z07 combined the z51, Fx3, J55 13" brakes, and oil cooler into a pakage called Adjustable Performance for $2550. Go to this link in the Action Center for a chart on all the suspensions in the C4; http://corvetteactioncenter.com/tech/c4/susp_chart.html
The 1991 was the stiffest of them all, as they softened it up in subsequent years. Its basically the same setup as the Corvette Callenge racing series cars sold in previous years.