I had a conversation with a Mopar block man in '74 and discussed this with him. Basically he said that Chrysler did a projection of how many vehicles of a certain kind they would sell for a given model year. Based on that projection, they would then produce replacement parts based on the number of vehicles projected to be sold and the historical consumption of that part. As examples he told me that more parts for the left side of a vehicle would be produced than the right side, fenders, headlight doors, taillight lens's, etc. He went on to say that a good example of this approach not working was when the Max Wedges were first produced. Chrysler produced a number of replacement cranks based on historical passenger car usage. When that stock was quickly used up due to racing service, Max Wedge cranks, according to him, were in short supply. That's what he told me, take it for what it's worth.