Customizing Model RR steam locomotives aka - Scratch Building or Cross-kitting is the process of creating a unique model from assembling parts and substructures from other modeling sources. This video showcases some example projects.
My dad built o guage brass locomotives. He bought lost wax castings and made the boilers and tenders from brass sheets. Some of his work was in model railroad magazine.
There is a factoid "blooper" in one of the model descriptions. (No, it's not the hyperbole that "Ken Kidder imported zillions ..." ) I will send a free lost wax casting (like a power reverse, generator, air pump, boiler front, etc. - your choice) to the first person who points it out. Email me: tom@clenet.org