I use k&s pipe bending springs. I heat the pipe up and place a spring inside and out side and only bend a bit at a time With the aid of a piece of dowel. After you have bent the pipes, sand them smooth and polish them with metal polish. Make sure you don't heat the bending springs, I've killed a couple that way. Hope this helps.
Here is the results. http://www.modelcarsmag.com/forums/index.php?showtopic=77442&hl=%2Bkenworth+%2Bt904 http://www.modelcarsmag.com/forums/index.php?showtopic=98361&hl=%2Bkenworth+%2Bt904
Ben