See the PDF link below for installing body mount coupler boxes, new trucks and wheel sets on Athearn Hopper cars.
https://images14.fotki.net/v1683/fileWc5B/a4014/4/4125954/16375553/airingAthearnHopperbolsters001.pdf (https://images14.fotki.net/v1683/fileWc5B/a4014/4/4125954/16375553/airingAthearnHopperbolsters001.pdf)
(https://images20.fotki.net/v1684/file3zP9/a4014/4/4125954/16375553/Athurncoupler.jpg)