Formerly a Williams brass USRA Mike; now a GM&O Heavy Decapod.
The sand domes were cast using 2-part mold material from a hobby shop. I found a loco in my collection (a Lionel SOU 4501-prototype Mike, actually) with a virtually identical dome, per photos of the GM&O locos, that was removable, mixed the material and formed it around the dome, dome-bottom-down.
Poured tin-antimony solder (from the hardware store) melted on the stove, let cool. Hard solder; durable. Had to dress the top of the dome (this was a simple, 1-part mold) to shape, then added brass or styrene (I forget) for the sand hatches. Detailing on the domes could have been further dressed/enhanced, I suppose. I was satisfied. Then epoxied domes in place on boiler.
Similar story on the steam dome.
This technique allows you to borrow shapes fairly easily.
I do table-grade modeling; if you are looking for Fine-Scale, this technique is probably too seat-of-the-pants. I'm happy with it.
