FYI,
* Jilles ran a standard issue T2'007. No prototype chassis, top deck or any other part. His setup was the standard issue with 3d of rear toe-in and 56mm tires. The extra 0.5d of rear toe-in was needed because of this years tricky track layout which required a VERY stable rear-end to keep it off the boards.
* Martin, myself and I think a few other team drivers tried a prototype stiffer top deck set. Martin ran it with his Mod setup and I ran it with my 19t setup. However, I believe we all went back to the standard top deck in the end (I know both Martin and I did). Not sure about the other drivers take on it, but IMO the car simply handled better with the standard top decks, which is a credit to Juraj's original design.
* I tried and I tried and I tried to get a one-way setup to work. And it did work...for an hour or two. But the grip simply changed too much each day and even after only a few hours. I have to admit, that any one-way setup for foam tires has very little room for big traction changes like at the Birds. My car was dialed on the first day of practice with a green track. But the next day the grip got higher and it was junk. Reworked it and it was perfect the next morning. Couple hours later in qualifying/practice as the grip changed again, its junk again. Same-same for the next three days. I then had a talk with Jilles, after the last qualifier
...put in a diff, 6d c-hubs and 3d rear toe-in...voila! Gained 2 laps in the main without ever having practiced with the diff and running so-so lines. For a one day race where the traction doesn't change much from qualifying to the main a one-way setup can be fast and consistent, IF you can dial it in quickly. But for the Birds or really any race/track that you don't have much time to dial in a setup for foam tires, IMO a front diff is definitely required. 
