I bought the MDC Shay Handbook after I assembled my Shay and the author does a very good job of pointing out places that need special attention. I opened a second kit and followed the author's instructions and it came out very good. It will creep at just over 1 volt @ less than 100 ma. If you are going to assemble a MDC Shay the Handbook is a MUST for proper operation.
I plan to add DCC to all 4 of my MDC Shays, there is enough room in the third truck for a speaker so three of them will have sound. There is absolutely no room for a speaker in the Two Truck Shay.
The Digitrax DH123 decoder will fit with a bit of a modification to the water tender as shown below.
The picture above shows the Two Truck Shay above and the Three Truck below. Both have the old Pittman open frame motor. The stall current is a bit under 1.5 amps, full load is just under 1 amp.
The picture above shows the Digitrax decoder, it has a bump under the text "ax" that requires a cutout in the top of the tender.
The picture above shows the decoder on place with the oil tank cover in place, the third truck tender supplies the water. The Three Truck Shay is a long haul locomotive, the Two Truck Shay is for moving logs at the cutting site.