[Tom Duff pointed out to me that the MIT TX-2 and the MIT Whirlwind computer were not the same thing. Whirlwind was used on SAGE (the semi-automatic ground environment), and it was the TX-2 computer that Dr. Sutherland used for Sketchpad. I had not been aware of how closely the TX-2 resembled or was a model for the original DEC PDP-1. Thank you Tom!]
Tom Duff also sent the following two links. The first is a collection of information about the TX-2, including Dr. Sutherland;s Sketchpad paper. The second has information about the Whirlwind computer.