Terry, I have in my possession another sketch of the Essex that you can throw into the mix. This one was done in the 1880's by former Acting Masters Mate Charles W. Fuller, at the time of his deposition concerning some cotton-stealing done by the crew of the Essex in 1864 (French-American Claims Commission, Oden Deucatte vs US). Unfortunately, the sketch is not detailed enough to be definitively "rounded-edge" or "straight-edge." And the sketch has the stacks too much in the center of the boat to be considered a really accurate depiction. But if you're putting together all the known pictures of the Essex, it might be interesting.
Will try to get it scanned and get a copy to you.