Note that the 1026 is already bowing upwards, a typical issue with the idler flats made from high side gons. Later, They bolted rails to the top of the deck between the needle beams in an attempt to strengthen the structure.
It has always amazed me that they didn't put rails the entire length of the deck as the failure point on these cars was usually over the body bolster. Maybe they were concerned that the pipe loads would hit the rails on curves if they ran them the full length of the car.
The later idler flats, made from box and stock cars had rails mounted under the side sills.