Forgot one thing that would make it easier - here are the number
series:

PRR 648314-648338, K7 (7/1950 - 15, none listed in 1/1955)
PRR 134079-135499, K7A (10/1963 - 3, none listed in 4/1968)
PRR 128079-129078, K8 (10/1963 - 2, none listed in 4/1968)


Ben Hom