Joe beat me to it. But to add his pretty comprehensive answer, here are the covers for the Aus. Atlas issues:-
http://www.ausreprints.com/content/main/?series=4194I'm certain these are landscape format and as the page says the comics are newspaper strip reprints, then I assume they are by Blummer.
The American issues are slightly confusing and I think Overstreet might have the info. back to front. The issue we have is #2. No indicia but there is a note on our page 46. Overstreet lists the first issue as nn and featuring a 28 page story tiled, "The Esmeralda's Treasure". These 2 make up the Avon run.
The Sea Hound from 1949, according to Overstreet, are numbered 3 and 4