If these documents were produced on a typewriter, the typewriter was not a Selectric. The Selectric does not have proportional spacing, the Executive does.
There is a Selectric that facilitates proportional spacing, but I'd bet my house that the "Selectric-Composer" was not used in this context.
The first IBM Composer was the IBM "Selectric" Composer announced in 1966. It was a hybrid "Selectric" typewriter that was modified to have proportional spaced fonts. It is 100% mechanical and has no digital electronics. Since it has no memory, the user was required to type everything twice. While typing the text the first time, the machine would measure the length of the line and count the number of spaces. When the user finished typing a line of text, they would record special measurements into the right margin of the paper. Once the entire column of text was typed and measured, it would then be retyped, however before typing each line, the operator would set the special justification dial (on the right side) to the proper settings, then type the line. The machine would automatically insert the appropriate amount of space between words so that all of the text would be justified.
THat's a lot of work for a private memo.