I don't know any details of this wreck on the SVRy, but based on the engine in the photo it may fit your time frame and the ties looks extra long for NG. The location I think is in the lower part of the Sumpter Valley which is now under the reservoir. I don't know anything of what might have been planed regarding std. gauging the line. Jim Grigsby being a retired road engineer might give you an educated asessment of how difficult it would have been to std. ga. with regard to the curvature as built. SVRy had lots curves up to and including 24 deg. especially on the Prairie extension.