I was also amazed by the amount of in-house manufacturing that Chevrolet appears to have done in the past. It doesn't say anywhere in the film where the individual bits were filmed but this was obviously in a time when cars were manufactured in a vertically integrated process. i.e. Chevrolet made their own cranks, pistons, engine blocks, springs, axles, etc. In modern times all those parts would be made by different parts suppliers on contract, often with multiple suppliers making batches of the same parts.
Chevrolet still runs engine assembly plants but the engine blocks are cast at a foundry contracted out from GM, rough castings machined at a factory contracted out from GM, and the finished product arriving at the GM engine assembly plants. The pistons maybe come from a different foundry, machined at a different factory. Same with the cranks, connecting rods, etc. The engines arrive wholly assembled for GM to bolt to transmissions (also wholly assembled at other GM factories, from parts that come from multiple different suppliers, etc.) and then the entire drivetrain unit is bolted into a car assembled at a GM factory.
The number of GM employees has thus obviously shrunk because GM simply outsourced all these jobs to different companies inside and outside the USA. You don't see the hot, dirty jobs done at a modern automobile assembly plant simply because they took those jobs and moved them elsewhere. I don't know if they did that to be flexible & competitive, but I'm sure that reducing the number of employees with high UAW wage scales had something to do with it. I worked for a parts supplier for Mitsubishi Motors North America and I can tell you I wasn't getting $23 an hour like the UAW guys on the line were earning.
