I also built a plane to have a go with but I decided not to bother after Guiness telling me the the FAI looked after all aviation records and they wanted me to pay for two officials to come from France to witness the attempt. They also would not rely on the Eagle Tree GPS and I needed to hire proper speed equipment which uses two beamed 'gates' a set distance apart. I guess all the red tape involved stopped Ali too.
They must have changed the rules, would be interesting to know which speed measuring method/device is now officially recognised by the FAI and Guinness.
Rob.