I checked Lloyd E. Stagner's book "Steam Locomotives of the Frisco Line" and whitewall's appeared in builders photos, but also in a couple of in-service photos. However, those in-service views were all from the 1910's; nothing beyond that decade.

Les

My guess is that the Frisco just “tricked up” their directly preserved locomotives (which doesn’t count the scullin steel switcher at MOT 3695, the “prison guard” 3749, and the eagle-picher Russian decapods) to add a bit of flair to their locomotives. I can’t attest for the others, but I have been able to find at least 4 locomotives the Frisco painted white walls on when the locomotives were donated to their respective parks.

This includes the aforementioned 1501, 1527 (I found a photo of it sitting in the Mobile yard in new paint prior to being moved), 4003 (being prepared for towing) and 4524 (courtesy of a very nice 12 minute video on the locomotive, which included film of it being moved to its current resting place).

So this would assume that the 6 Mountain types, the 4 Northerns, and the 5 mikados all had white walls painted on them when they were put on display.