You probably already have this book -Along the Trail with Lewis and Clark, by Fifer and Soderberg.
For other people planning to follow the route - I bought it on Amazon in 2013, the second edition dated 2001, but info is fairly timeless. It includes the historic highlights followed by "Touring Today" sections for each leg. Included campgrounds of all sorts which helped me find some great spots to camp by the water where they also did.
Also it helped me find a number of state parks, monuments and museums that mark their journey. For anyone trying to figure out where today's roads & monuments are in relation to the L&C routes eastbound and westbound, this book has very detailed maps.
We followed their route only as far as Pompey's Pillar so have lots yet to enjoy. Gave me goose bumps to see Clark's signature and 1806 up on the rock.