I have a suggestion for a destination on the route. The Levi Coffin House is considered the "Grand Central Station" of the underground railroad:http://www.waynet.org/nonprofit/coffin.htm
Located in Fountain City, Indiana, it's about a 100 miles North of the Underground Railroad museum in Cincinnati, OH.
There are several good resources for pre-existing routes in between that I could help connect you with.
I live in between in Richmond, Indiana. Here we have a nice multi-use trail that could be used for part of this leg: http://www.indianatrails.org/Cardinal_Greenway_Richmond.htm
This trail rolls right through an important piece of history. Richmond is the "Cradle of Recorded Jazz". At Gennett records, Jelly Roll Morton, Louis Armstrong and others recorded.
You can see some of the buildings where this happened:http://www.starrgennett.org/
The bike path rolls right through the remains of those buildings in that (beautiful) gorge.
A local foundation is working to establish a related museum, which is currently in progress.
Let me know if you want more help mapping this leg of the journey.