Thanks to you all. I found basically the same stuff about emdash and hyphens, and where I had used hyphens when a 'change of thought' occurs have changed them to em dashes using —. But I agree with Jelby about having a space on both sides -- I think it works better on a narrow page.
Anyway, I'm about to upload the second version of The War Prayer having corrected the typo, centered the headings, and put a little more space below the headings.
But I haven't added a full line because I don't like too much blank space on my Cybook screen. I'm reading a book now which often has gaps of 20% of the screen in the text, and I think it looks ugly.
I'd appreciate feedback on the second version.
On a more general topic I'd really like to see a sticky with information about recommended styling, or even perhaps a seperate forum for newbie publishers. Any takers?