The one piece frames that Chevrolet made in 1957 for the passenger cars are not California frames. They are just supplied from a different Chevrolet plant. Many1957 Chevrolet cars built in the Oakland CA plant do not have one piece frames. Same goes for the Los Angeles plant. One piece bumper's are a California thing, in case of a crash, they needed to separate the cars fast and the one piece bumper's allows the car's not to get tangled together in the event of a crash. Domenic