there were clues leading to this failure that went uncorrected---the ill handleing, the toe in issues,---they should of raised an eye brow to something beyond a different toe setting--

the king pin area likely failed because of the method and quantity of material removed to get the chrome out of the king pin boss, the tapered bolt for securing the kingpin was over tightened causing the fracture--when the king pin boss failed the car was out of control--this led to further damage breaking the axle at the perch area---
Axles mounted like that with split wishbones need some rubber ends on the links to allow for a little flex/bind issues--the use of hard ends/heims will put the axle in a very high stress every time it moves in any direction