you asked if 55 had the push button on cars no it was keyed.a funny thing in the early (55+) gm s if you just turned the switch off and not lock.someone if they knew it was easy to jump in turn the switch and bye bye car.the keys were another thing there was a limited number cut thus my 54 caddy key would start my brothers 55 chev convertible led to some head scratching when filling up 😀 back then it was easy to park back where it was