The documentation says that if I apply the 'header menu' custom template to an Auto-Nav block, it will change from an unordered list to a Nav-bar style list. I am trying to do this in the main block, but it stays as an unordered list. I tried this on Plain Yogurt. It works in the header block.
Try it in Header Nav area, you can get the exact output. Header menu custom template will work in Header Nav area.