The answer to your question is: "Yes" and "No".
There are three number series of interest: GN 72500-72749, GN 72750-72770, and GN 72771-72773.
The latter two were made up of cars pulled from the former, and were the ones used in container service. So that's a qualified "Yes".
The "No" comes up because, first, the cars apparently got roller bearings fairly quickly after conversion. Also, all the pictures of these cars in Thompson's book show additional reinforced ribs on the car side (2 per side) (see my photo). He shows three shots of the container cars with the reinforcements. But he also shows one shot of a car in the "regular" series with the reinforcements. As you know, Sunshine did these cars. It would appear doable to add the reinforcing ribs. I don't think Sunshine offered this version, though I could be wrong.
I am attaching two overhead views of the car and the containers. From the pictures, I don't see that there was any modification to the inside of the car for the containers.