What is the range on the Chris Craft?
Down river is likely an option as the current
will boost your fuel
efficency but up river can be hard. Most folks do the great loop so they only take the river in one direction and come back up the east coast
North of St. Louis, it's easy to find marinas
and haul outs and the locks tend to keep things under control pretty well (Mother Nature can still make it hairy at times but much better controlled in general).
South of St. Louis, there are no locks and the river tends to run fierce (it can change dramaticaly by season though). There are very limited docking
facilities south of St. Louis with long distances between them.
While it certainly can be done and there are people who do it, most cut up the Ohio
River to the Tennessee River and take the Tenn-Tom down to Mobile. If you are set on doing the return trip by river, you could go down the Mississippi
and back up the Tenn-Tom route
and bypass much of the fight against the current
"Great Loop" and you will come up with lots of reference material as it is a key part of the trip.