IKJH345's comment seems most logical as I cannot find a W section of that size anywhere, but there is an "ST 6 WF 13.5" listed in the 1949 edition of the 5th edition of the AISC manual:
A = 3.98
d = 5.98
Wf = 6.5f = .400
t stem = .240
Ixx = 11.4
Sx = 2.39
rx = 1.69
yx = 1.21
Iyy = 8.3
Sy =2.55
ry = 1.44
The same member is listed in the 1956 printing of the fifth edition and the fourth revised printing of the 6th edition (1967), around the time you mentioned of the building's construction. All the material properties from this edition are the same as listed.
Mike McCann
McCann Engineering