wierd build sheets found in my L78

[Tarrytown SS427s]

Very cool! I've seen these in Framingham Chevelles before, and almost every vehicle built at South Gate, CA. I never understood the reason for codes such as M21, when that piece of paper was usually deep inside the seat, before the upholsterer knew what kind of car it was destined for. I'd love to know who wrote these out, and at what step in the assembly process it was done at. Consider the rate these cars were being built at, and that's an awful lot of writing each day!