Just a quick update. I decided to make the two articles as separate as possible. One covers patternmaking, the other doesn't. One only briefly mentions necessary sewing tools, while the other goes into detail about what supplies you need. The parts that absolutely must overlap will be trickier.

I went ahead and pitched the article to the magazine. An assistant wrote back almost immediately and said she'll pass the idea on to the various editors and they'll get back to me, but it might take a few months. I hate waiting that long, especially when I know I'd get a much quicker response from the other magazine, but I'm just going to have to be patient. I want to give the national magazine first shot, since they (probably) pay more and the publicity is greater. Once I know what slant they want me to take for their article, I'll be able to write the other one, ensuring that it's different enough to pass.