Jason,
The first 4-wheel flats and 8-wheel flats, boxes and stock cars are believed to have been built by Billmeyer and Small, which was painting the trucks the same color as the body in 1872. The 2nd and 5th boxcars in the Delaware River bridge photo are 22' cars from 1872. The rest of the box cars are 24' cars and are probably all Great Western Manufacturing built, although the two on the right may be new Ohio Falls built cars. Although the trucks on all cars are in the shadow, the Great Western probably followed the example of the 1872 cars.
The 1st boxcar appears to possibly have swing motion trucks and the 3 cars on the right have common sprung bolster trucks.
Be cautious of the boxcar at the Leavenworth Museum as it was poorly documented and was cobbled together.
If you want to share more Kansas Central information, get in touch with me. Presently, I am working on trying to get drawing sets together for KC #3 and #4 2-6-0s.
Dave Johnson