We rode in a gm bus when taking the Ford plant tour about the same time as Dodge. Some smart as pointed that out to the tour guide. She answered we were riding in a giant mustang!
I worked as a mechanic at a GMC dealer in the 50's. We had a customer that transported new Chrysler products. Chrysler insisted that he used a Dodge truck instead of his GMC, so ... he changed the cab to a Dodge.