Dave
Being an SP knut, I have a amassed an in depth Southern Pacific library. I have many books on SPNG and other NG lines too. I don’t think you’ll find a better resource than the aforementioned book, 378 pages of pictures, diagrams and useful documentation of all things SPNG. If you can’t find what you need, let me know as I have lots of reference material that may help, i.e., specific OEM truck information.
While I model with 1/32 & 1/29 equipment, someday I intend to integrate/model narrow SPNG in to my pike. As I recall O gauge rail works out nicely for NG track and such with 45mm track, someday I hope to get there. My bucket list is already an overflowing 55 gallon drum. Keep us updated on your endeavors please.
Have fun,
Michael