Re: not "outside admission"

While an excellant book, yhe reference to "outside admission" valves is probably incorrect. While it is true that the later rebuilds had their piston valve centerline's outside of the cylinders, they would not have been considered "outside admission". Most engines with piston valves were considered "inside omission" - the live steam being admitted in the center of the spool. One of the advantagees of this is that the piston packing was only subject to exhaust pressure. The bolt-on slide valve conversions were "outside admission", necessary due to the original arrangement of the steam ports.
I believe that the reason for the evolution from locating the piston valve centerline from "inside" to "outside" was to simplify the valve gear connection.