Here's what I was told many moons ago. The 464 had sat derelict at Durango for most of the 60s. During that time, the superheater elements were removed and sold to a local lumber company that needed them for their locomotive boiler that was being used as for stationary steam supply. The lumber mill was in the "Farmington area." When Knotts bought the 464, it needed tube sheets and was missing the elements, so the decision was made to make it a soak. The 128 pound boiler pressure came from the State inspector who determined (after the boiler was re-tubed) that the butt straps on the boiler courses needed "one more row of rivets" That's all I can recollect now and some or all of it may be folklore! Can anyone out there add to this?