The Dallas Morning News found and interviewed Marian Carr Knox, the secretary to Lt. Col. Jerry Killian, and she says she never typed the CBS-Bush memos. She says she would have been the one to type them, and that, in her office, she used an Olympia manual typewriter - and only later an IBM Selectric.
I have an Olympia desk type typewriter of proper vintage, so I pulled it off the shelf and took a look. It looks just like the one on mytypewriter.com. One item of dispute is whether the numeral one on the CBS-Bush documents was typed with a separate numeral one, or by using the ell key. On the Olympia, there is no separate numeral one.
Another point of dispute is whether the superscript "th" contained in the CBS-Bush documents could have been typed. Ms. Knox says her typewriter had a "th" key, and indeed mine does. But as you can see from the greatly enlarged image below, the "th" on the Olympia has a striking feature - it is underscored.
There's no underscore visible on the CBS document. The character also does not extend above the 187 as does the CBS-Bush document.
I retyped the 18 August document on the Olympia. I printed out the pdf file from the CBS website, and then rolled it into the typewriter. I used the CBS document to set the margins on the typewriter, then removed the CBS document, rolled in a fresh sheet of paper, and typed away. Here's the result:
Now I'm not as good a typist as Ms. Knox probably was. I got an extra space between the 18 and August, but still, you can see the spacings are entirely different than the CBS document.
I'll admit I'm not an expert of any kind on these matters, but the two examples certainly look different to me.