Google proves itself more useful when they began putting up archives of old newspaper microfilms. If you want to see how comics looked decades ago, this is the place. It's a bit of a pain to use, but it's worth it.
One of the papers Google is archiving is St. Petersburg Times. One of the strips they were running was Kelly & Duke (back then, the title was just Kelly). Here are some daily samples.
Note how the artwork has more detail than the later run.