My understanding of "Umlaufblech" is very similar to your transation. "metal sheet that goes round" meaning the part of the chassis used as walkway, and also to append or mount various fixtures, that goes around the boiler, on the two sides and also on the front (I hope I'm understandable)
Also, Stehkessel should be the rear part of the boiler (where the firebox opens), but I don't know the correct english term for this.