A married couple made that drive in an amphibious jeep back in the 50s, and wrote the book 20,000 Miles South about the trip. It’s years since I read it, so I don’t remember if they had to go by train or boat to get past the Darien Gap. I do remember that they decided not to try to take their vehicle out into the ocean because of weather.
I recently read about an attempt with a fwd vehicle and it took them months to make the 90 miles. Of course they were slowed down by threats from guerrillas.