Driving all the way from Brazil to the US should take at least three months, if you place the vehicle on a ship in Caracas and skip Central America. First you'll have to drive south into Argentina, then up through Chile, then through Peru, Equador, Colombia, and Venezuela, where you'd cross the Gulf of Mexico from, and finally arrive in, say, Florida. There's some dangerous territory across Colombia, because of guerrilla warfare. Of course, you could also drive north through Brazil, crossing the states of Pará and Roraima, and then into Venezuela, but the roads up there are much worse, although probably much safer than driving thru Colombia.
The Brazilian Kombi is a very old project. It is an updated version of a 1957 design. You can see one in "Little Miss Sunshine", though probably an older German-built model. It is not a very safe vehicle. It is rear engine and head on collisions are often fatal, as the driver is not well protected.
Getting visas to drive through so many countries should also prove to be a bit of a headache. I wonder how easy it is for an US citizen to get a visa into Venezuela these days.
Anyways, if I were you I wouldn't take this trip alone. It would be too risky. You should take at least one or two friends along. You could also start a blog to keep everyone posted on how your adventure progresses.