I seem to recall reading about one. And in: https://multicians.org/chrono.html there's this entry: "08/65 GE 635 delivered to Project MAC". Clicking on the 'GE 635' link leads to "MIT's GE-635 system was installed on the ninth floor of 545 Tech Square in 1965, and used to support a simulated 645 until the real hardware was delivered." Noel