I just received two rapid replies from the Corps. of Engineers. Haven't been able yet to find an Archivist to ascertain
July, 1863 data.
From the Corps.
"I'm checking my nav charts but I'm having trouble finding Port Hudson*.
Either way - we may have to estimate since the river has changed course a
couple of times since then."
"Vicksburg is at River mile 436 - The northern tip of Baton Rouge (where Port
Hudson historical site is) is at River mile 235 - so based on today's mileage
its about 201 miles."
* Note, Port Hudson is no longer on the river due to river course changes and
does not exist as a village any longer.