Given that "engineer" in those days practically always meant a white man, especially to the class that the advertisement was meant to reach, the heads are at least somewhat varied in age and hairstyle. The hands are probably the hardest thing to draw, so they were likely copied from a reference photo or sketch a bunch of times which does make them very similar.
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The weird similarity between the engineers make it strangely look like it is AI generated (although it is not).
Given that "engineer" in those days practically always meant a white man, especially to the class that the advertisement was meant to reach, the heads are at least somewhat varied in age and hairstyle. The hands are probably the hardest thing to draw, so they were likely copied from a reference photo or sketch a bunch of times which does make them very similar.