Re: D&RGW mikes

If you want a serious history of these locomotives buy the Grandt Line book "Mudhens". Great history and lots of pics. Also they just reprinted it so it is possible to find again. There was another book about the 463 and it's rebuilding and history that had a lot of good technical information in it, but the title fails me right now. It also had a history of the early CATS, maybe Mr. Cook knows the title.
The Vulcan compounds were rebuilt because they were a complete failure with saturated steam. At the time the best alternative was piston valves and so all the 27's were rebuilt with D-valves. After the 28's were bought the D&RGW rebuilt some of the 27's with a piston valve arrangement and super heated some of them. The inboard and outboard piston arrangement was dictated by the type of valve used on the piston. The slide valves engines were cut up in the '30s. All of this is coming from memory so there may be some errors.
Paul