There has been a lot of speculation on the printers used for this, some even speculating typewriters. I've read discussion across a lot of sites, and, from my tech experience, and knowing GM (why pay 1000 typists when you can spend 800 times that on a mainframe and some printers) i'm betting that this was the series used:
http://en.wikipedia.org/wiki/IBM_1403
others have more info on this, but i haven't found anything that confirmed that, other than a gentleman on a forum claiming to have serviced them, but didn't remember the typeface used.
Here's a link to a similar discussion about font and machines used:
http://nastyz28.com/forum/archive/in...p/t-46459.html
And here's a guy working on making a font matching that typeface using the output from an actual IBM 1403, and his sample looks pretty good:
http://slantedhall.wordpress.com/201...e-in-progress/
Another link from someone else about the same project:
http://brainwagon.org/2013/01/23/an-ibm-1403-font/