I can't tell you about the process, but I emailed some Brazilian consulates in Argentina and one of them (Paso de los Libres) answered that you can apply from there (the others have still not answered).
Update: Puerto Iguazu consulate informed you should apply in the country you have residency. Go figure...
Update 2: Buenos Aires consulate informed you can apply from there, but all your documents must be notarized (with an apostille).
Update 3: Córdoba consulate informed you can apply from there. They also provided a link to a page with the necessary documentation (in Spanish).
Moreover, you can apply from Brazil, as per the official resolution. The information in the article you provided is wrong. And, as you are American, you can enter in Brazil as a visitor without a visa. Given the current conflicting information provided by different consulates, this is the path I suggest you to take (unless it's not a problem for you to come back to the US and apply from there).
Regarding the notarization of the documents, the resolution does not demand that (see the update above). But if it is not very difficult for you, I would add any official stamps I could on my documents just to be safe.