Two other excellent threads that might interest you:"Combination" is alterately used with "Consist" and "Construc(t)" (all used as nouns) as meaning the layout and engine combination and arrangement of any train, freight or passenger. Wheel layouts on steamers were generally mentioned in far more specific terms and included a name given to that arrangement and boiler/power, such as 2-8-4 Berkshire, 4-6-4 Hudson, 2-8-2 Mikado, 4-6-2 Pacific, etc.
Spaw