setting ideas
Okay...so you've got the NP passenger cars. Now that's a great starting place for a bit of research into choosing a possible locale, which can influence planning choices on scenery, place names, tunnel portal style, rock type (granite, limestone, etc.), tree type (conifers, hardwoods, etc.). All this can work to provide a cohesive feel to the layout to give it that 'right' look. You know, perhaps not prototypically accurate, but certainly it gives you and whoever else sees it the feeling that this layout has its own character and identity.
As for motive power - a pacific would look great with that train, but perhaps a USRA Mike would do better on those grades. Keep the turntable size in mind throughout the loco shopping experience. Didn't the NP use Geeps on their passenger trains when they dieselized?
Keep up the great work and as always, thanks for sharing.
Galen