Years ago ( I guess we tried to emulate the trip of the Che ) we rode bikes from Buenos Aires , down to Bariloche , crossed to Chile , up the coast through Peru, Ecuador, Colombia ( the coast ) , boat to San Andres , then Venezuela, Brasil ( Nothern shore ) to Bahia, down to Rio, all the coast down Uruguay ( Punta del Este ) to Montevideo, Colonia then Ferry cross to Buenos Aires.
We did that in a full summer vacation ( Dec - March ).
We were riding Honda XL500 registered in Argentina, we all had ( 3 ) Argentinian ID and was kind of lenghty to cross the borders, but as said before MONEY and patience ( mostly money ) gets you an easy cross.
Back then Paraguay was a tad unstable and certainly we wanted to stay clear from Bolivia ( specially SANTA CRUZ de la SIERRA )
Our dream back then was to make it to California but Panama was an issue so we headed east from Colombia.