Sorry for a cross-post.
On the GM&O 51000 series boxcars, the Railway Prototype Cyclopedia #19 comments that the GM&O considered these war emergency cars a 'structurally defective design' and allocated a number to LCL traffic to get the best use from them, for this purpose they got a couple of extra grab irons to the left of the door.
However, I believe the last was listed in the ORER in 1972, it seems they cannot have been too 'structurally defective'. But RPCYC #19 also says they were rebuilt as the 22500 series cars in 1963.
I am not sure whether it was the rebuilt cars that lasted till 1972, or one in original condition.
I'm wondering if anyone can cast further light on GM&O's attitude to composite boxcars? Unlike IC they do not seem to have had many, so did they consider all composite cars 'structurally defective'?