All interact spindle motors were rectangular (squarish) in shape. How old is your machine?
The original Interact 4s had Contraves spindle drives. The later ones had KTK.
Somewhere I remember reading that some of these motors came from Italy.
From a old maintenance manual, the contraves drive used a Contraves GF-112M10BF9 spindle motor (DC), part 21551211, and armature brushes were part 21551261, tach brushes were 21550345, tach assy 21551234.
From my KTK notes, the spindle motor was a 6P4QXX with the XX denoting the KW rating of the motor, part 21551235, armature brushes 21551259, tach brushes 21551260, tach assy 21551257.
The changeover happened (in theory) in Sept of 1987.