I think my older brother had a Buick automatic that had the starter button under the accelerator pedal. You had to have the transmission in neutral/park, and then you pressed the accel. pedal to the floor to start the engine.
Prokop: Did that key have to be turned, or just inserted? Did you have a separate starter button? The indent obviously opened some contacts and gave you tactile feedback. Perhaps the flange below the handle fit into a slot that turned when the internal mechanism was at the proper spacing. When I see something like that, I just wonder how it works.