Hello @pennsyfan
Finally got to my train room to check the cars. It's so far from my house; it must be at least 25 feet from the back door. I hate it when life gets in the way of what's really important.
I checked the FRH and Williams cars for differences. The FRH car is a reefer and has reporting marks 62587 on the end (the FRH cars could also have 97477 as reporting marks). The Williams car is a boxcar and has a reporting mark of 587477 on the end. The Williams car also has dimensional data on the door and an airtank and braces on the bottom of the frame. Here are the two cars together: the FRH car is on the left. The Williams car has glossy paint, but that could just be because it is MIB and the FRH car has been out on my layout.
Just to complicate things, I also have a KMT boxcar that is the same except the car is silver. No reporting marks or door dimensions on this boxcar. It's a little hard to tell from the photo but the car is definitely silver and the others are white. Other than the color, the KMT car is more like the FRH car. I should have taken a photo of all 3 cars together. Sorry.
Good luck deciding what you have.
Regards,
The other Bob