Banks did not go to Fort DeRussy, he went to Marksville. Only Shaw and Moore went to Fort DeRussy, and that was unplanned. If you would get a copy of the 1863 Avoyelles Parish "Captured Confederate Map" from the National Archives, you can match the road on that map to a modern topo map and that will tell you exactly what you are looking for. There is also a very detailed series of maps of the whole retreat from Alexandria to Simmesport, but I don't have the details handy of where those maps come from.