If portability is required, the only thing you can realistically do is simply pour the text in. Let the reader determine how to treat paragraph breaks, whether to justify, serif or sans-serif.
I agree in principal, but oh! part of the enjoyment for me in re-habbing public domain books is to give them some fancy chapter heads, formatted quotations, etc. I do feel, as do many, that the main body text should be left up to the reader, but is there any harm really in specifying a fancy font just for chapter titles? Otherwise, we all might as well just load up Project Gutenberg plain-text...
'Twould be nice if there were a way to offer *all* readers an option to use the publisher version or their own preference, that was actually *easy to use*.