Sounds familiar...
I am pretty sure thats the same car as this video. I have a customer who runs my engine in dual AX/ DE events in that region and to me, that sounds like one of my engines.. His car is also yellow AFAIK.
He is ONE HELL of a driver and if you look close the tach can be seen mounted in the same place on the dash as the car in the video.. Note that the tach STARTS at 5,000 RPM.. The engine is good for 8,700 RPM. Powerband is between 3000-7700 RPM.
http://www.youtube.com/watch?v=y13C3v2L788Here is his first outing on the big track from a while back, same engine.. Dual purpose BEAST!
http://www.youtube.com/watch?v=1uFRrbjy_pMThere is a chance that it isn't the same car, but I doubt it... He never sent me pics, but from the way this guy drives and the region and engine sound it damn near has to be.
That stumble you hear is the fuel spilling over the floats in the carbs as the G force impacts it, especially at lower RPM.. It makes the engine go full rich for a second, then it screams to life. That could be tuned out with float height adjustments, or by going to a pair of Dellortos from the Webers that it currently has... Just little old 44s breed that beast to 218HP. IF its the same car/engine that I believe it is.