Here's a question: how do these rules differ for SHORT STORY manuscripts? I heard that magazines still want the older style (Courier, underlines, title near the text not at top of page, etc). And how about POETRY? Scant little current info online about these things.
There are two ways for me to answer your question:
1) If you are submitting your short story or poetry to a magazine, which would be the most appropriate venue for it, carefully read their submission guidelines. If you can't find them, email them and ask for their submission guidelines.
2) If you are submitting a short story collection or poetry collection to a literary agent, don't. Unless you're really sure they accept that. As in, they specifically mention of their website or on agentquery.com that they're looking for short story collections or poetry. In which case, regular manuscript format with the different selections as characters is a pretty good way to go.