That is great! I was talking to another forum member about making these cars and was (still) looking at the Atlas 89' foot flatcars. We were also looking at containers, but undersized ones from Lionel and MTH, and gluing a thin sheet of plastic on the outside to give it the smooth look of the AFT equipment. I like how you sanded the braces down but would need to buy the sander and make time for it (maybe I'll stay with the plastic sheets).
Waiting to see your finished cars.