South America has more Italian-based groups rather than Italian-Argentinian\Brazilian\Etc hybrid ones.

Due to the drug trade, and the Italian-style political curroption, all Italian groups are believed to be pretty active down there. Mostly Calabrians and Neapolitans.
Also a LOT of Italian fugitives have been captured while in South America (Venezuela, Brazil, Uruguay).

Here's the link to a post by Furio_from_Naples with maps taken from Mafia Export.

- As far as the Italian immigration is concern:

The Southern American culture was way more similar to the Italian one. The was no need of creating a ghetto, a\k\a "Little Italy", like it happened in the USA\CND\AUS or even Germany and Belgium.
Few Italian areas were established of course, but there was no need to, compared to the other countries listed above...there was less (way less) discrimination.

Language, way of life and even genetic features were more similar to the one of the many Italians, so assimilation happened right away.
I mean: imagine being an Italian immigrant of the early '900s, with strong mediterrean features, moving to, let's say, Kansas City...now THAT will be a cultural shock.
Now you're the same guy, but instead you're gone to Venezuela...still different from Italy...but not that different.

And yes, the large majority came from Northern\Central Italy. Not that this bunch had NO criminals...but no historic criminal organization.

Even today (words of four college mates of mine all from Argentina, all with Italian lastnames), very few people call themselves "Italian-Argentinian", simply because their ancestors integrated faster in the local society.
These four guys were AMAZED when I brought them around our area and they saw a local Italian folk feast...with 2nd\3rd\4th generation Italian-Americans celebrating their heritage.
They even told me that, back home, during the world cup GOD FORBID if you cheer for Italy...especially if you're in high school or college!

Compared to the USA\CND\AUS and many other European countries, Visas and citizenship were easier to get too.

This are my two cents.