I have one of the Warrior Run 6500 flat cars, great kit! I have one truck assembled, and I replaced the cast springs with real ones. The truck is still just glued together, the springs are just there for looks. The frame is assembled, and, here's the interesting part...
I also bought an AMS flat car body - without trucks - to take the K-Brake equipment off of for the flat car, since it comes without brake gear. It occured to me, that instead of throwing away the flat, I can splice it with another AMS flat car - and "simulate" a 6300 flat! Although I think to be accurate, I'd have to rearrange the stake pockets and add AMS reefer trucks to it.
Thanks, Robert