Greg,
Thanks for posting that link. A very interesting article. Too bad the 3511 has been out of service for at least the last 10 years.
I'm not sure if the Class 26 "Red Devil" is serviceable or not, but here's a shot from 1999 when it still was. The second engine is a standard 25NC, and as you can see, the gas producer firebox in the 26 means no smoke. The "Red Devil" was always hard to get good pictures of for that reson.