These appear to be automatically generated from sites such a Project Gutenberg. I don't know if these are even the best "computer generated" versions in .prc form, but they might be because MobiPocket does not provide Linux tools for conversion (which prevents some sites from producing MobiPocket files).
The
Portable Library includes manually formated versions of the Harvard Classics, but they are 99c each. I think they are worth the price, but they are also encrypted which means they can't be read by FBReader. This is not the only version of Harvard Classics, see an earlier
thread for alternatives.