Tim,

There's a Dick Kuelbs photo of GN 25947 on the MKT in Dallas, TX in 1961 on page 17 of Great Northern Equipment Color Pictorial, Book One - Box Cars and Stock Cars, by Scott R. Thompson. Granted, this is a USRA clone built 1923, but it is in revenue service, and is not labeled for hide service.

There's a J.W. Mathews photo of GN 25063 (a clone) at Wenatchee, WA in March of 1961, from Richard Hendrickson's collection published on page 138 of the Second Edition of Lines East, by Patrick C. Dorin. It is in revenue service, not labeled for hide service.

I have a photo in my collection of  GN 24667, which is one of the USRA cars, with a 4-62 reweigh date, taken 1962 in Baltimore, MD, by Joe Collias. This car too is in revenue service, and is not stenciled for hide service.

I do have a Joe Collias photo of GN 25183, one of the clones, taken in 1963 in Watertown, SD, labeled for hide service. 

The cars are all in the postwar overall mineral red scheme, with the "Great Northern Railway" herald.

One caveat: GN did replace the grab iron "ladders" on the cars with actual ladders in a post-WWII reconditioning of the cars, but they kept their wood running boards and Murphy XLA roofs.

The GN did use these two series as stock for 1950s rebuilding programs that resulted in stock cars, and many were converted to MOW bunk cars, etc. in the 1950s, but my July 1960 ORER lists 264 of the USRA cars and 367 of the USRA clones in revenue service.

These are the latest surviving revenue service wood sheathed USRA cars I am aware of.

Regards,
Bob Heninger
Minot, ND