How about just set up the radar gun and have guys fly at it?? There are so many combos out there, and no rulebook guidelines, that it's gonna be right hard to set up any format. A relaxed, run what ya brung format would be a lot of fun. A nitpicked-to-death rules bending fest would be about as fun as camping in an ant bed.

FWIW, Radar isn't an approved method of measuring speed per the FAI. The Budweiser rocket car supposedly broke the sound barried years before the current land speed record holder. It was timed with USAF Doppler radar which sounds like it's pretty accurate, but the speed was not recognized since it was based on Radar.

A lot of the small planes are very hard to get an accurate radar fix on, and the speeds vary widely from reflections off the prop. But setting up a timed speed trap is a lot of work, radar is much easier.