Sounds exciting. I don't know anyone, but there are several pages about this in Portuguese. If you don't get enough feedback, I may be able to translate a couple of pages. One of them includes a map that shows long stretches of unpaved roads, and also the times between towns:

The description of the ride (trip segments on the menu in the right):
http://www.descubraminas.com.br/dest...id_pagina=1614

The map:
http://www.descubraminas.com.br/comu...formato=grande

The times and distances
http://www.descubraminas.com.br/dest...4&id_pgiSuper=

If you go, I hope you get to spend some time in Rio de Janeiro, catch some live samba and/or chorinho at night -- it is a beautiful city!