I found my copy of Hidden Treasures: The Story of the Ohio River & Western Railway by Edward H. Cass today. It was by my bed where I had been re-reading it. I love this book! It's a shame it is out of print. Maybe Timber Times will bring it back!
With a large Coca-Cola and a hand full of peanuts, I browsed the book carefully looking at each of the photos as I searched for flat cars. There were several photos and a hand roster to go by.
While these don't give me everything I need, they are close enough to build the model. There are many other pictures of gondolas and box cars of the same size to infer braking systems and other things. The internet didn't turn up any other good photos.
Next - drawings!