Old Eyre Highway???

From the little bit of it of what I saw at the start of the year when we went out to Koonalda homestead, and from what I have heard, yes you can travel along it, albeit at a reduced speed compared to the new highway, but it is still very much doable.

Hema Atlas shows some bits of it either side of Nullarbor Homestead. You could use Google Maps to find bits of it. If you zoom in you can find where the tracks take off the highway. Just right click on the junction and select "What's Here" and the co-ords for the way-point will appear at the top of the map.

Nullabor to Border village, would be the best section. Stopping at Koonalda, approx half way, for a break.
You could then return to the highway( 7 klms), or continue on to Border Village.
Just my thoughts.