If you go to the ROAR website (www.roarracing.com
) and click the Rules link on the left side navigation bar, you will be able to see the 2003 ROAR rulebook.
On pages 43 and 44 they list the rules for off-road buggies and trucks. For trucks, the body rules state "Off-road Truck" so I am guessing that means that only truck bodies are allowed.
Hope that helps.