The source of the image made on an IBM Selectric Composer was the printed manual for that IBM typewriter. A scanned image of the manual may be found at here. The manual (as stated in a note on its second page) was actually typed on an IBM Selectric Composer in order to demonstrate its capabilities. (As the note explains, the large-type headlines in the manual were not typed on a Selectric Composer, but everything else was typed on that machine).
But the question is not whether the memo was typed [as he says] or prepared or set [as the manual says] on an IBM "Selectric" Composer, the question is whether it was printed by one.
Besides, all this turd would have had to do was simply consult the "welcome.htm" page written by the maintainer of the site to learn that even that fellow doesn't believe the Killian memos are genuine:
Q: Do you think that the IBM Composer was used to produce the documents in question.A: No, I do not. And my reasons are more practical than scientific. Let me explain. First, the IBM Composer is NOT a typewriter for general use. Those who used it were typographers/typesetters and were trained on its usage. It contained no error correction capabilities as modern typewriters do. The keyboard was somewhat rearranged from the standard keyboard of a Selectric typewriter. The ribbons used on this machine were specialized (and expensive) ribbons that produced very black output used for reproduction purposes. The machine was extraordinarily expensive. The odds of the military providing anyone, other than someone in a publications department, with a machine like this is unlikely. It is unlikely that Killian would have made the effort to make a superscripted "th", but not pay attention to basic spacing around a comma. My opinion is not a political one, rather it is just based on knowing the difficulty of using this machine, and knowing that it was found mostly in print shops, typesetting shops, small publication offices, and occasionally a law firm, but I've never heard of one on someone's desk (who wasn't a closet typographer). Even if Killian had asked someone else to type it for him, requesting that it be done on an IBM Composer would be like asking someone to phototypeset a memo on a Varityper. Its not practical.