Will certainly involve some bad roads and some marine transport (no road from Panama to South America.
We have driven most all of Mexico and Chile and a few hundred KM's in Central America.
Like you, we also had aspirations of driving all the way. But, with the multitude of different border requirements, and lots of miles with little of interest, we made alternate plans.
We flew to Santiago, Chile, rented a car for three weeks to drive most of the country, getting as far south as a little past Punta Arenas where the road ends. Then, back to Santiago and flew to Buenos Aries and took a cruise south around Cape Horn and up the coast of South and Central America to Los Angeles. Yes, including a stop in Ushuaia and the short drive toTierra del Fuego. About the same price we had budgeted for a drive all the way.
We did this trip two years ago.
Ex: 2003 Alpine 38FDDS. Ex: 1997 Safari Sahara. Ex: 1993 Foretravel U240