I did the rear motor case mod like kraig listed above and also one using one of the printed brackets being sold. I feel the non-printed route is the way to go. Everything lines up better and the trans spins much more free. My printed one didnt quite line up perfect and always felt hung up.
The pics on petit are great, explains it clearly.
Pics from races show the team drivers running a lay down and new chasis. I hope they come out. I recently ran the TND lay down kit on turf and it seemed pretty good. I need to work on my setup some as the rear was too loose and laptimes suffered some.
Best the car has been for me is with the 3 gear case, but I'm going to put in more time with the lay down. We'll see.