There was a story awhile back where a man slowly over times changes a female into a guy. I would also love suggestions of other stories where a female is turned male.
My own story The Winsome Widow contains a scene where a woman astral projects into a man's body. I'm sure it's not the same thing, but you might still enjoy it.
I'm actually a really big fan of these types of stories but they are sadly few and far between. An author I really enjoyed was "Trapper Jock McIntyre." Wrote some promising starts, however the author definitely finds the act of women wearing men's underwear and jockstraps the biggest turn on, so the act conversion, which I find more interesting, and the sex, again which I find more appealing, doesn't get as much attention.
Other things I found:
The Taming of Lou: sadly very short and light on sex but full on conversion
My Boy at the Poker Game: already a FTM but very hot none-the-less
Transforming the Toy
Sadly, that's all I've really found so far. If anyone has more suggestions, or if they're interested in working on a story, I've got a few ideas.
There is a series called Modified (6 Chapters) by KegRoller. I only read the first chapters, where a female student wakes up with a penis and is revealed to her sorority sisters... Not really my thing, so I stopped reading and am not sure if the transformation will go through or whether she will just stay with the penis...
Don't know if that meets your criteria, but it's not too difficult to get a little bit into it.