In 1976, Checker Motors began manufacturing parts for GM. I remember seeing open rail cars delivering sub-frames to the Van Nuys Plant. Hemmings had an article about parts that Checkers were making for GM:
https://www.hemmings.com/stories/how-checker-remained-in-business-after-the-end-of-taxi-production-building-everything-including-the-kitchen-sink/
Very interesting info!
The assembly plants were still paying outside suppliers by check when I worked at Van Nuys. When Corporate sent out an advisory that fraudulent invoices were being sent out to various locations, I asked about an invoice we had recently received from Checker Motors. I was surprised when I was told that they are one of our best suppliers.