Southern Pacific ore cars prototipe question

Model Railroader Prototype information for the modeler
1

Hi

I am interested in the Athearn set of the SP ore cars 94988 and 94943 .There is a difference in this sets one has high side the other one low sides I know from a previous post that this cars were modified from low sides to high in the mid 1960’s for increased capacity by SP

Does anyone know what exactley happened to this ore cars when exactley were modified how long it took and if all of the cars were modified at once?

I am trying to establish which of the models low side or high side are infact prototopical to model in the time period of 1965

Thanks very much for your helpfull reply

stefano

2

…or infact has any pictures with date/s close to time period 1960 to 1965 ?

thanks