Steve---Thanks for sharing this. I would love to see the display myself.
One thought--it was not too completely unusual for streamlined trains to be hauled by steam, esp. in the early days (though it is worthy of mention--in fact I did not know that the Portland section was hauled by steam at first myself---i.e.,this old goat learned something from you!!).
And for a train to be hauled part of its run by diesel, part by steam was not unknown.
Diesels and streamlining were invented about the same time, it is true, but they were, after all, separate inventions. World War II slowed down production of all rail equipment. Some trains might have received both diesels and streamlining sooner than actually happened, and also more simultaneously than actually happened, had finances and energy (taken away by the war effort) allowed it.
Some early streamliners had steam locomotives rebuilt to a streamlined appearance just for them.
Soon enough, by the late 40's and early 50's virtually all trains in the country were diselized but many of them never became streamliners.