I spent a good few evenings modifying a brass switcher from an oil burner to coal and adding sound.
Before
The main alteration was to unsolder parts of the tender and build up coal doors and add a coal load, followed by some heavy weathering.
After
The hardest and most time-consuming part has been to get the Tsunami chuff rate matched with the wheel rotation across the speed range, as the gear ratio in the loco is very low - about 12:1.
You can see the progress for yourselves with the usual video clip.
http://www.youtube.com/watch?v=299O74FakYw
Jon