Todd, you're probably correct. My guess was based on the proximity of the wreck to either Dundalk Marine Terminal (Baltimore) and the port of Philadelphia/Camden. The St. Lawrence Seaway opened in '58 but I doubt that a steel shipment would have gone up into the Great Lakes and be railed back to the east coast.
That being said, some of that type of steel is only produced in a few mills in the world. Even now, some of the big guys don't want to be bothered with special alloy material and it's just that the packaging looks exactly like the stuff that comes in from Europe and Asia today.
Also, if you look real close at the photo it appears that the black B&O  Gon 352409 resting above the red car has the same cargo. You can just see the ends of similar cases sticking up above the top of the car sides indicating that the cargo was loaded transversally.
What I'm a bit hazy on is the width of the interior of a gondola of this type. The bars I'm referring to are about 8-10' long and fill the cases end to end and are usually wrapped in the case with heavy water resistant paper.
We may never know for sure.
Best regards,
Dave Lawler