I had the same type of problem with a UP 4-8-4' s tender with the 14 wheel arraingment John.
I like Ray's plastic wheel advice . I think they would have to be smaller in diameter though .
My issue came on backing up the tender through some O31 switches. I tried everything to get the issue resolved . I even made a deep radius on the inside and the outside of the non flanged wheels. Somewhat succesful , but still had an occasional issue. I finally gave in and replaced the 14 wheel arraingment with 2 six wheel trucks ............ No problem since, but to the person who wants to keep everything prototypical its a big nada.
I'm glad you had the photo of the wheels because it reminded me of part of the problem.........that front four wheels that rotate against the wishes of the rigid ten wheel arraingment had a tendency to put sideways pressure on the tender and make it jump the track or drag on part of the switches.
I even thought of switching the front two rigid flanged wheels with the second set of rigid non flanged wheels but never tried it.
Good luck
