Credit Where Credit's Due
All of the covers have come from the Grand Comicbook Database at
http://www.comics.org/
One of those places that makes you glad for the Internet.
I found these Aquaman splash pages (um... never mind) on
http://www.eskimo.com/~tegan/aqua/rev/index.html
This is probably the best of the images I used as a reference for Black Jack, from a story in Adventure Comics #150 (March, 1950).
Here's the Sea Demon.
Here's King Yascom.