There's all sorts of parts that they share through the years. Most years have some unique parts, but, suspension, brakes, engines, transmissions, rear axles, etc. fit more than one year, or even several years in most cases. "Early A-bodies" have generally included '60-66 models, but, even '60-2 models have parts that don't interchange, so, just how far do you want to break the definition down?
