One thought I had for the 52 pin D-sub were the two 50 pin Pertec tape interface cables in some "cabinet kit" packaging for under floor. 

Saw this at Fort Monmouth Cecom on an 11/750 from a military project for early office automation on System V Unix based off of 2.x Unix work at Hanscom AFB called Lonex (if I remember the acronym).

Bill
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