At long last, after more requests than it should have required, I've corrected a long-standing oversight and created a short story manuscript template for Microsoft Word. You can find it at this page:
After you customize the template with your own name and contact information, you'll be able to create properly formatted manuscripts with ease. And the template even includes a wordcount field that updates on request, rounded to the nearest hundred.
The template should work for all versions back to Word 2007. If anyone is interested in a template suitable for older versions of Word, please let me know. I'm sure I can kick one out sometime in the next decade.