I don't have your specific fic (and I'm miffed that no one has posted a link because it sounds interesting). However, I do have a genderswap/transgender fic to recommend.

Don't Call Me Daughter (http://deewinchester.livejournal.com/2000.html#/2000.html) by lavinialavender. It features one of the best 'always-a-girl' Deans I've read. Heartbreaking but oh-so possible. It could've gone this way.