The PRP comes with a 3mm upper and lower deck with additional cutouts in the bottom to remove weight. It is a complete redesign. In addition to the two chassis plates you get side impact protectors with aluminum standoffs and hardware, the Truspin plate that sandwiches the spur gear between the plate and the aluminum input mount for better gear mesh and no flex, titanium hinge pins that are longer to accomodate a longer wheelbase or shorter wheelbase if so desired and a set of roll center adjusters. I have yet to loose a spur gear in 6 months of racing, still running the stock gear but I have had the Truespin plate on the car the entire time.
The Pro4 is race ready out of the box. You dont have to have all the bling like delrin diffs, alum caster blocks,etc. For carpet I would suggest 3mm chassis plates and a BRP bumper then go have fun!!