It's worth a good deal, Jim, I was hoping you might weigh in.
I've read The Unexpurgated Carl Barks and the Coo-Coo facsimile that Hamilton published a while back (I think both are still available from the publisher) but would still have a hard time being certain about these covers. His early work seems like it is in a lot of styles and all over the place. My interest in this magazine stems more from my interest in early humor/girlie publications - I'm as of yet no Barks aficionado or anything. These later Red Pepper annuals surface from time to time on ebay, so they probably had a decent circulation, but considering how many years it was published, monthly issues of the Eye-Opener seems fairly scarce.
Here's an image of the annual for the following year after which most definitely is in a similar style. The date on this (1937) is after Barks had moved, but I'd wager the magazine kept plenty of his work on file...
http://i42.tinypic.com/10yf4et.jpg
I saw a nice cover on a monthly issue that a seller recently advertised as Barks work. I think the issue went for like 80 bucks, which shows what tagging a big name on your auction will do (random issues of Calgary Eye-Opener seem to go for about 10 dollars, about like Capt. Billy's).
http://i39.tinypic.com/21o7uw4.jpg
I've noticed Barks has a thing for harems, so I've got no problem with the attribution