I was working for a tow company years ago when I heard the story about a guy with a 55 Chrysler 300 that had a dead battery. when the tow truck showed up he suggested push starting the car. The driver said OK but you'll have to get up to about 25 or 30 before that works. He gets into the car and looks in the mirror to see the tow truck backing off a half mile so that he would be up to 30mph when he started to "push" the car
LOL Really though you could jump them off with a 12 volt system. I did it several times on our old wagon. That old 55 very seldom let us down as far as actually quiting and breakdowns. It could be a pill to start especially when it was real cold but that was the nature of a 6 volt systems of the day. Oh yea one notorious fault of old Plymouths was the gas gage. IIRC if it read half a tank it was empty.
I still have the steering wheel center cap off our old 55 Belvedere. It has a ship in the center of it.