I can tell you from personal experience that flat cars need to be loaded in
a balanced manner....
....I have two 7 1/2" gauge flat cars equipped with pivoting boat seats for
riding cars. The first has a seat that has a more or less central column
pivot and is bolted to the center of the car. It tracks very well and does
not cause derailments.
The other has a seat that has the support column aligned at the seat back
but it is also bolted to the center of the car. This puts the weight
distribution more to one truck than the other and causes the car to derail
frequently to the point it is unusable in its purchased configuration and
has to go back into the shops for a new seat (repositioning it is not a
solution as the seat needs to be able to pivot for backup moves).
When you are the load in question the distribution of weight causing
derailments becomes a matter of great interest!!!
PS- Yeah, I know, but even a heavy duty depressed center flat would have the
same issues for those thinking about a comment about excessive loading!!!