This is what the letter page letterhead looked like for Batman in 1976. However, the white part is where I whited out the top part of a letter that was there and was not part of the letterhead.
By the time 1967 rolled around Lana Lang was an important character in many of the Superman titles. Espically in Lois Lane's book. She was so important that for a time they used the above letterhead on the letters page. I have always wondered why Lana Lang never got her own series.
In the early 70's when DC comics started publishing the original Captain Marvel again. Some readers were debating on if he was better then Superman. Of course this was an old debate as it was going on when Fawcett was publishing the Captain's adventures. This letterhead is from a 1974 issue of Superman.