Is there a publication that goes into these "vehicles" in depth? I was looking through "Outlaw" but was not satisfied with the coverage of the subject.
PM me an email address and I can provide some (slightly incomplete) rules I created for a GenCon event long ago that was an 'anything goes' chariot race.
You'll probably have to fill in some blanks and tweak things a bit, but it might give you a good starting point for chariots at least.