True. They did mass produce them and they all (or mostly all) worked OK. But think about a few things. First, If you got ten answers from ten people on the right driveshaft length, you'd probably get ten different answers. Hard to tell which cars have prior accident damage that might not have been straightened out properly. Hard to tell how a motor is mounted (or if the motor mounts were off a bit due to poor Chinese quality. There are probably a lot of other factors that could cause measurements to vary from car to car today, but 50 years ago, on the assembly line, Ma Mopar had the advantage of having brand new cars rolling down the assembly line that pretty much had to be straight and true.