there is an article about Chuck Aarons Red Bull 105 in the newest issue of vertical mag (read it online for free at verticalmag.com, need to sign up though).
Apparently his machine is modified quite a bit. According to the article, it has stiffer blades, running at "very high RPM", a pressurized fuel system for negative G maneuvers, and a far forward CG, to make it easier to recover from unusual attitudes.