The L29 has a total loss air system for the brakes
True, but it also has an emergency system, and pressure gauges for both systems. So no real excuse for running out of air.
Rumour has it that an expert in jet operations from CAA advised the pilot how to get data to check if the machine could be flown from Dary Flat
Unnecessary. All the data you need is in the Flight Manual, which (should be) on the aircraft. All you need is the runway data.
FWIW, basic takeoff distance (sea level, etc) is 600m.