When did IC start modifying their 50' SS DD boxcars into single door cars?

Charlie D modeling the Mopac http://mopac51.tripod <trduck@...>

October 1989 Railmodel Journal (on page 45) shows an IC SS DD boxcar converted into a single door car (IC 34899).

Does anyone on the list know when IC started this program. I model circa 1954 and was thinking of changing the Walthers 50' kit into a single door version and wanted to see if it fit my time frame.


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