I concur with El Coke on the 476 comments.
People often ask "What was your favorite engine?". In my Dgo. years I may have had varying opinions of that, based on the latest performance of an engine, but hindsight is always clearer and I can say without a doubt that the 476 was my favorite for both running and firing. It had an uncanny abiity to roll very freely and smoothly, no matter how often the drivers were dropped and boxes rebuilt, side rods rebushed, etc. The main consistent malady I recall was that it would "lope" as it lost steam admission from one port when it was up in the higher notches of the quadrant. Some of you may recall hearing it blast up Hermosa Hill on three exhausts occasionally if a hogger didn't keep it down just one below the "company notch". I used to think that the radius rod/tumbling shaft assembly was out of kilter from one side of the engine to the other in light of the fact that it would run very square if you kept it just below that notch. However, in light of Coke's reminder of the saddle working in the frame, I can well imagine that may have been the culprit, as I would figure it causing the same symptom.
It was also the most consistent in firing qualities and could really get down and grab the iron even when boiler pressure did wain. I hope it finds it's way back to faithful service sooner than later.
Jeff