Very cool project. Wish I had the time for that kind of work these days. I did the research and artwork for the 3rd Rail model and that was a lot of fun but not the same as a classic kitbash. As you are aware we did the pre-1955 "as-delivered" paint scheme. The UP Yellow scheme would be nice on a set of these as well as the simplified later orange and black.
What are you using for CAD software?