...get on that Forney build too, but dont freelance, get a real feel for the design, the designer and the style by researching and building a scale model of a historical piece...push your skills to build it right and not let the model take control of itself to become another freelance shortchange.
I realize that most freelance models are abominations. Some such ride-on live steamers just make me want to vomit, but then most real
locomotives were damned ugly, too. You've cherry-picked the finest examples of the locomotive designer's art, to build your most authentic scale models.
I'm still a student of all this. I am
seeking to learn actual locomotive design practice. I've already noted a few discrepancies from such practice, in the Disney engines and elsewhere. For example, real peak-roofed cabs commonly(although not universally) had very shallow peak angles- much shallower than those on the WDW engines.
I'm clearly not a spit-on-the-sidewalk modeler. I like my trains beautifully designed, colorfully finished, and tastefully coordinated with their consists. That's part of why amusement park trains appeal to me. But also, the park scenario gives me an opportunity to practice my locomotive design skills. Also, parks offer the model railroader huge interest in the most limited area. Witness Sam's Natures Wonderland ride model.
Walt Disney and Walter Knott both got involved in locomotive design. With your knowledge of William Mason, I'd bet you could also come up with some great new designs. I invite you to give it a try.