Wish that I could help you on this, but right now, I'm as much in the dark as most here. One guy who likely could help is Sammy King in CO if you could contact him. He spent a lot of time with 204 and 205 at the end of steam charters down there. By that time, boiler pressures have been cut substantially due to deferred maintenance.
My last visit there was in early 1977 and 204 was the engine used on a Howard Thornton Mid West Rail charter out of Texas. 177 miles from the border to Guatemala City and the engine did really well. We even passed some slow trucks on the adjacent highway between Santa Maria and Escuintla at 4:30 in the morning.