Fenton,

A little more data.  I checked my January 1952 ORER, and the GM7O had 6 ex-Alton 17000 series boxcars listed.  They were not big cars: 12'-1" at the eaves, 12'-11" over the running board  and 2730 cuft..  By comparison, the 1937 AAR standard boxcar was about 14'-8" over the running board and 3712cuft.

Todd Sullivan