I think the 400E was a little different. Brass trim with black boiler bands. Interesting because date of production puts it in a time frame when 400Es had Nickel trim and black bands. For the custom order they could have replaced the Nickel trim with brass and left the boiler bands black.
The cream or Ivory windows on the cars were not one offs for this set although rare. I have seen boxes for state cars labeled Ivory trim.
They did everything in every color why not this. A trim color change. A little change on the engine. a special 20th century limited box. I would even throw in little 20th century limited red carpets.
Like Norm who lived in Syracuse at one time. I still live a few miles from where this set spent most of its life.