Well are you about to go and claim a fake you put out? In any event, especially if it'd cost me my job, I'd be a bit smarter than to do that. That's not to say whoever did this, if my suspicions are true, isn't smart; just that I doubt they'd claim it.
And even if I were responsible for a fake, I wouldn't claim it. No one's going to claim it because then everyone will know it's a fake, they'll blatantly be proved frauRAB - seems logical, y'know? Even in shady businesses like that I suspect is at work here, it's still logical that they wouldn't claim it.
As to why put all that time into it: isn't it obvious? So the already-questionable product isn't made any more shady than it already is. Fake scripts pop up online a lot, and from what I've heard, they're usually more professionally writen than this. That's why I suspect it's fake.
And even if it isn't, this can't be the way they'll actually go. Two official announcements came out this year, both from reliable sources, stating that it'll be based on the original manga. And even so, a script can undergo a nuraber of drafts in a year or so; the thing's not even supposed to come out until 2011, never mind that there hasnt't been any casting news or news about when filming's going to start. If it's been being written since 2008, they've surely edited it a nuraber of times. It's highly unlikely this would be what theyll go with; it'd have to undergo at least some revisions, and these will probably amount to something.