Photo taken by Nick Schmiedeler in September 2018
BH Photo #434735
I agree with your theory. Railroads were very into reusing spans that still had some life left in them. In fact, this article is a very interesting read:
I believe I have a location where this truss could have been moved to:
This is also a 140' truss (the measured distance between the east abutment on this bridge and the western pier, which appears to be a former abutment). Located Labette County, the bridge was relocated there around 1953. I've found that sometimes bridge parts could be in storage for several years. I believe there is a good change that the Salt Creek Bridge could be the original location.
Thinking about this....
Frisco used quite a few ~100-foot truss spans, and the stone pier on the west bank looks wide enough to support a truss. The 52-foot spans look older than 1951 but Frisco moved steel spans around quite a bit. Possibly the new piers and used spans were moved in to replace an old truss.
Former Frisco bridge on Carthage-Wichita line. Frisco steel bridge book says two 52-foot DPG and two 25-foot I-beams, installed in 1950. Not clear if that's the bridge or just the I-beams but the pictures look like just the I-beams.