In the newest Railroad Model Craftsman there is an article on copper concentrate cars built for the Santa Fe and Southern Pacific. What is of interest is the Frisco ordered 4 modified cars (#s 63900-03) of this design in 1967 for hauling lead concentrate in the lead belt. Anyone have any more info on theses cars (i.e. why only 4 cars and how long did they last in service)? Any photos? Thanks. Larry F.