i.e. Completely Open, and Restricted to certain mods...
that way you cater for both degrees of people, everyone can compete with their existing vehicles (regardless of modifications already performed on them), and if you don't have a whiz bang truck - you can still compete in the Restricted class.
too easy

If this is the path we chose to take - then rather than trying to come up with rules that won't see yourself being kicked out of a class due to wrong engine type, wrong suspension type etc - then lets work out what the restricted rules should be (knowing that anyone can compete in the open class)...
what do people think?
I know this will mean more rules, but i think it will be easier than banning the people who are going to set it all up from competing.