I bought the MTH Legacy SD70ACe in SP colors in scale-wheeled, fixed-pilot version with the desire to install the hi-rail wheels. I using past-tense for a reason...the model came through with some quality defects that disappointed and I traded it back to my LHS for the ABBA N-S F7 Restoration model. So I never did get to convert the wheel sets, but I did get a chance to run it on my layout.
I have all Ross track with the minimum curves of O-88. The wheels held the track okay, but derailed in the switches due to the oversized hi-rail frogs. In other words, without modifying all the switches by instally a shim in the bottom of the frog to keep the wheels from falling in and then going in a different direction, it really DIDN'T WORK very well on hi-rail track in my experience.