Your biggest obstacle may be in the smallest numbers anyway. Below, I highlighted in red something you may want to check into before you go any further. This is from 9 years ago:
Class 3
"Vehicles built from a 4-Wheel drive utility type vehicle. Vehicle must have been series produced in quantities of at least 5,000 units within a 12 month period and be readily available to the general public in the U.S.A. Must be a 4-Wheel drive vehicle capable of being driven through all four wheels."
Class 3 is the domain of short wheelbase vehicles like the Early Bronco, Bronco II, Jeep, Kia Sportage, and Chevy Blazer. Known for a brutally rough ride, Class 3 none the less remains popular in desert racing at large, but has recently seen a decline in entrants in the SCORE series.
Often built on a low budget, Class 3 makes an ideal entry point for new racers. The broad, open rules of the class have resulted in some impressive suspension configurations, and suprising performance.

Here is the link: http://www.off-road.com/race/981k/html/program1.html