So I asked an acquaintance that is a CNW expert, and according to him, there were certain classes of heavyweight so painted. The diners on the Northwestern Limited, a block of sleepers, and commuter cars rebuilt with rollerbearing trucks.
So the take away to me is that those classes were painted yellow to back up the lightweight cars in the 40's and 50's. There was not a mass repainting of the heavyweight fleet, nor was any ordered with the yellow, so it wouldn't be prototypical to run an entire train of heavyweights in yellow.
That said, those cars were a nice find and it's your place, so you can do what makes you happy. They are by no means a gross misrepresentation of what happened (IE the tyco GG1's on tri-mount trucks in New Haven McGinnis paint - that is out in space, your cars are not).
https://thumbs.worthpoint.com/zoom/imag ... 81e298.jpg
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