I just purchased my first InterMountain PS-2 4750 18 rib covered hopper. The model is great, but being curious, I went on line to lookfor photographs of the prototype. Much to my dismay I found numerous photographs of this car but with the train air line running along the outside edge of the cars. The model has it running through the spine of the car. I found two photographs which appear to have the air line routed as in the model, a BN and an IC/ICG I think. Will someone explain the difference? Was it railroad peculiar, a modification in later production orders, or a maintenance change, etc., or is the IM model incorrect? Thanks in advance.