Re this book(and ABC story)
A Self-Made Man - Woman Goes Undercover to Experience Life as a Man
Has a man ever infiltrated a female group like this and writtten about it?
Adam’s Apples likely preclude this.
Wear a turtleneck.
Not written and not in real life, but guys passing as girls on internet games happens often, with different success and trouble. The biggest rules of thumb are: if she’s got a waist too small for two kidneys and boobs large enough to serve as flotation devices, it’s a guy. If she’s dancing naked, it’s a guy. If she complains about chainmail bikinis, it’s a girl. If she complains about another girl char in the same clan wearing a chainmail bikini… husband and wife 
I actually was a part of the case I know best. There was a clan in a game I used to play, and this clan was 8 guys and a girl (Tys); one day, a new player (Blade) joined and got intruduced by Tys and a clansman (Kal) as being his girlfriend. Tys and Kohr (Kal’s brother) were gf/bf.
Blade played for nine months before posting in the forums an apology from the whole clan. It turned out that Tys and the brothers had been having an argument because she said that female players got treated very different from male ones, sometimes consciously (people coming on to you), sometimes unconsciously (two players whose toons had identical stats, the one played by a guy gets chosen for the role most likely to get rewards - although the female player had performed that role to perfection when she didn’t get passed over for a guy). They didn’t believe her. Tys worked with Blade to make “her” pass, ensuring that the clues that yell “hi, I’m a guy!” wouldn’t be there: Blade’s physical look was chosen by Tys; other things were just things to “not do” (do not say “ewww” if the rest of the group is girls and they mention their periods, for example).
It had taken less than a game session for the brothers to be convinced, but they’d decided to continue the experiment to see how long Blade could pass.
As one of the girls in the game, I can say that we sometimes remarked that it was unusual for a girl to play Blade’s class (rogue); a couple times another girl and me told Tys “it’s funny, but some times I find myself thinking of Blade as a ‘nice guy’ and then go and smack myself.”
There were times when people made a list of the best leaders in game, and the names tossed were all males; I’ve seen some guys make the list of “the best three leaders” after several months not leading. Then a female player would ask “so what about Nava, Kiri and Blade?” “oh yeah, they’re great!” “so why aren’t any of you mentioning them?” We never got an answer about why.
Nobody minded that Blade was a guy; among other things because, since Blade wasn’t the flirty kind, “she” hadn’t broken any hearts (there have been cases of guys falling for a “female” player and later finding out it was a guy - those aren’t pretty).
Billy Tipton did it for decades. It was big news when he/she died in '89 and the truth came out.
Mrs. Doubtfire and *Tootsie *don’t count I assume 
I should have been more specific. I should have asked if any men did this as a journalist and reported back the same way he author did re a man’s view of how female groups interact within themselves.
I’ve seen this book at the library and the original hardcover really makes me wonder how she fooled anyone.
http://a5.vox.com/6a00c22523c18d8fdb00fad68ba57d0004-500pi
Maybe the effect is different in person, but I imagine a lot of people “knew” she was a woman, but no one said anything because men don’t do that.
Bosom Buddies
To say nothing of Some Like It Hot and White Chicks.
But no, I don’t know of any male journalist who’s done this.
I suspect that too.
I don’t know of any male who did what Vincent did. Sometimes a male journalist will dress as a woman for a day to report on how uncomfortable heels and hose are, but that is hardly at the level Vincent went through. It’s usually much easier for a female body to pass as a male than a male body to pass as female. Unless the man doing the investigation was slightly built and fairly young and really careful, his cover would be blown very easily.
Anyone else think she looks more macho in the “before” picture
than in the “after”?
People fill in the details with what they expect. If you meet someone who claims to be a guy and dresses and acts like a guy, you make the assumption it must be a guy. Then, you focus on any features that look masculine and use them to support that assumption (good old fashioned confirmation bias). Maybe some people would have thought he was gay or something, but I doubt anyone jumped to the conclusion that he was a woman.
On the other hand, the picture on the book does just the opposite. It says that it’s a woman and shows you a feminine picture that lets you emphasize the feminine features in your mind. I’ll bet you that if the pictures and title were reversed (claiming that a man was disguised as a woman for the report), that you’d be saying “They must have known she was a man all along.”
I thought she really pulled it off and would fool a lot of casual lookers that she was a guy.
Then I realized I was looking at her “before” picture.
Not necessarily. Have you ever seen Ann Coulter’s neck? Either she’s a man who’s successfully passing as a woman, or some women have Adam’s apples.
OK, maybe not that she was currently a woman dressed up as a man. But I say it’s impossible to look at that picture and not think that that man used to be a woman.
Extraterrestrials are different.
Regarding the OP: Apparently some people thought she was a gay man (straight guys tend to think anything less than 100% macho is evidence of gay). It would have been interesting if she had actually joined a group of gay men. My guess is that some would have thought she was a FtM transsexual.
If she wants to be taken as a true biological male, and not a trans female to male I’m guessing this would be MUCH more difficult if infiltrating a gay male group vs a hetero-male group, as gay men (in general not always) would be much more attuned to people shifting gender.
Maybe… I found myself instantly thinking “Edward Scissorhands” and I don’t question whether Johnny Depp is male.
And Billie was a girl who posed as a guy. The OP was looking for guys who posed as girls.