RYPN link
I cannot speak about when or why these cars were stored in Mount Union, but a cut-and-paste from a thread on RYPN linked above on page 8:
"They are standard gauge US Army Transportation boxcars. Do not know their history prior to arrival at the EBT. Story #1) They were purchased by Kovanckick Salvage in the early 1960's for resale, but they have cast iron wheels and ceased to be interchange compliant and so were stranded. Story #2) USATC was paying Kovalchick to store them but they stopped paying. When pressed about rent, they transferred the cars to KS in lieu of rent."
The second link below is my photos from October, these boxcars appear in photos #6, 7, 9, 11, 13.
boxcars before scrapping photos
Matthew