It is legit, I've gone over the entire modification process myself. (All last night) It took 3 months to do. And in order to fit all the boards into a lower profile area all the caps had to be removed and have right angle connectors installed for the lowest profile assembly possible.
Very real people have been doing things like this to the reg xbox and a lot of other game systems... Its a really cool mod I saw it over on Xboxscene a fourm I belong to.
Here is the guys work log.... http://benheck.com/Games/Xbox360/x360_page_1.htm