The books from IA tend to be scanned images of a page with a very poorly OCRred text page to allow for searching. Unless you are heavily into masochism, I would avoid trying to do anything with them.
And again, since there is an epub version of the book on Gutenberg, why not simply download that instead of saving the web page version and converting to epub? This link should point to
Before the Dawn (epub) which I find much easier than messing with conversions.