Thanks very much for posting this. I was about 3 roads through doing a similar canvasing myself.
As you mention, 800 of them were rebuilt in 1939 to an interior height of 10'0" with steel sides, Youngstown doors, and AB brakes. Several others were decapitated and placed into coke service, with others cut down for use as wheel cars.
I've yet to see a photo of a C&O single sheathed USRA boxcar with a shop/reweigh date after 1930 which did not have a radial roof. (The 1191 also had one.) Part of this is due to a severe lack of photos. The lone article in the C&O HS Magazine regarding these cars (Nov/Dec 2014) does not provide any further clarity regarding the roofs. It does however note that 1191 was shopped in 1931 for "major repairs", so there's always the possibility it and 632 are outliers.
The 1924/25-built ex-HV cars (C&O 82000-83999) went through a similar rebuild cycle. Many of them were shopped in the early 30s and received radial roofs. There's a great sequence of photos in the COHS archives showing several dozen at Raceland in various stages of undress/rebuild. These were once again rebuilt in 1941 to receive steel sides and other equipment. The newer of the 36' cars (84230-86999) also went through a similar rebuild in the early 30s where most received radial roofs.
So, based on those other contemporary early-mid 1930s rebuild programs, and the scant few photos available, I strongly suspect the C&O's USRA cars all received radial roofs of some form prior to the heavy rebuilds just before the war. This is still mostly conjecture, and I'd love to see evidence to the contrary. I suspect we've seen all of the photos that we'll ever see of C&O single sheathed USRA cars that were taken between the early 1930s and their retirement in 1950.
In a way this is good for me, as there were only 8 cars left in 1947 - my earliest operating year - making them numerically irrelevant for my fleet. (And I've already got one of the Westerfield kits in the pipeline, so....)