Okay it might not be the "Mother Road" but until our French cousins renumber many of the Routes Nationales to Departmental roads, RN43 still exists and runs from Calais to Metz.
The trip may have to be undertaken in the car rather than the bike, but it takes in places that have figured heavily in 20th Century French and World History.
I'll see what there is to see along the way... Ligne Maginot, Vauban Forts, Sedan, Malmedy....
So far I have this as the route from the Shuttle terminal and the start of the N43 near Calais to just outside Metz when it eventually runs out and joins the N3 for the run into the city.
As for the way back? I have no idea.