Until now we mostly followed the Route National 1, which used to be a real road (dirt). Although some of the original parts probably no longer exists. Detours ar formed when the road gets impassible and sometimes the detours then become the main road. The only railway they even built here still exists and connects Kananga and Lubumbashi. I think train rails just made for a convenient building material. Many of the bridges have been fairly recently (20 years ago?) rebuilt by the missions.
So no, I do not think these road we rail road beds.
With regards to questions about our vehicle: fire away. Our website contains a fair amount of information on the car too:
www.radiobaobab.be , then click on the UK flag (top right) for the English version and then choose "The car" in the menu. Our website is terribly outdated and due to get an update and revamp.
Our car is a simple affair compared to some of the rigs on this forum. But it worke very well for us.