If it is stamped SAC Latta on the inside of the mag well it is postban and will need to have the muzzle device removed and replaced with a legal post ban brake or have the threads turned off.
And as you already know it will have to possess the correct U.S. parts count, 7 U.S. parts with a brake, 6 without.
Tell your friend to go to www.falfiles.com for more info.
I am always leary of the Rosario guns that are supposed to be pre-ban because I have heard of guys welding over the post ban importers marks (SAC Latta in the mag well), re-machining, re-parking, and selling an $800 dollar gun for $1500.
Edit: One way to spot an illegal gun that has had the import markings welded over is to inspect the park job really well where the markings usually are. The park color will vary with the hardness of the metal. If it has been painted over park, like a lot of the south american guns come, you can't see it.