X950-956 ballast cars

Another mystery of NG Land?
In her book Narrow Gauge to Cumbres, Doris Osterwald noted that the C&TS received 2 ballast cars (she separately notes 10 drop bottom gons so I assume that the "ballast cars" are not DBGs). I also find in the D&RGW RR Summary of Equipment listings for both January 1, 1967 and January 1, 1969 7 ballast cars X950 - X956 (under NON -REVENUE EQUIPMENT (NARROW GAUGE)). Are these the cars that Doris refers to? I have never seen photos of these cars nor observed them anywhere. What are they? Did the C&TS really get 2 of them and, if so, where are they?
Thanks in advance for any info on these critters,
Dick Ferguson(Fergy)