@PRRronbh The video of the blooming mill at Weirton Steel (not sure if I'm ok to link it here) makes it look like ingots were arranged side by side on the car when they're at the stripper. You can see them rock side to side in unison when the mold gets lifted off them.
I bet most of the single row ingot trains were on narrow gauge rails or were very large ingots. I know some of the sprue plates we made where I worked would likely have fit well on a standard gauge flatbed car.