i can't see the pics, or even the link, but one thong does seem pretty clear to me

the rules state that you need to keep the orignal bits of the car that are strutural
so the inner wings and stuff need to be kept original
the floor of the car has been deemed to not be required (or whatever he's chopped about) and so it's ok

if you build a car, then decided to entre events because it's a good motor then don't be surprised if the car doesn't meet the rules and they don't let you play