Do you have any specific model numbers for "3D
graphics terminals"?
I am drawing a complete blank on the product numbers (5xxx series?)
but IBM made a series of CAD workstations in the mid-80's. A friend
of mine ran a lab full of them at the University of Wisconsin - Milw
for the Mechanical Engineering department. I didn't think they were
IBM RT based.
http://www.cadazz.com/cad-software-history-1980-1985.htm
Is sort of interesting, too.