What say you? Is this a '56 or '66? It seems as though the underlined/raised numbers were more indicative of 50's and those without the underline more indicative of 60's, but both versions occurred in both decades. The size being smaller than the D or same size as the D is also supposed to be a hint, but it isn't clear to me if it's the number itself being smaller or the combination of the number and underline being smaller. I'm leaning towards it being a '66, but wanted to see what those with more experience have to say.