my experience in 2004
Don´t know if it is too late. I did that trip in december 2004.
The route was:
Santiago - Mendoza (Arg) - Neuquén - San Martin de los Andes - Osorno (Chi) - Pto Montt - Chaiten (by ferry) - Cohcrane - Bajo Caracoles (Arg) - Calafate - (Perito Moreno) - Pto Natales (Chi) - Estrecho de Magallanes - Rio Grande (arg) - Ushuaia - Pto Natales - Pto Montt (in 3 day ferry) - Santiago.
Aconcagua is amazing. The carretera Austral is spectacular. It took one month.
Most of the carretera austral was gravel at that time, I don´t know now.
I strongly recommend it.