[GreenKeys] Xerox used teletype model 35 but not ASCII or (the case of th...

[Jim Haynes]

Yeah, the RCA Spectra was basically a copy of the IBM 360, with some
changes that made it a better machine but prevented use of IBM's
operating system.

It's very possible that the machine never had an LESU.  (L for Model 28,
ESU for electrical service unit)  It's not an essential part, just a
convenient place to put the line relay and its power supply and some other
options.  So Xerox may very well have ordered the machines without LESUs.