Respectfully, equipment like that is not unusual at your level and subject of government employment. And being the Navy Dept. In the military food chain, the Navy is as far above of any States National Guard, as a baleen whale is to plankton.
As a government installation, it is quite possible that the Texas Air National Guard had a few Selectric (or its successor models) in its possession.
After my six years active army, I spent two in the California National Guard Nike Hercules program. This program was much higher profile than any armor or infantry guard unit and was "Full Time" like the Air National Guard. Long story short, it was unusual to even find any kind of electric typewriter, let alone an IBM "Selectric".
Given my two years of experience in the "active, full-time", Nat. Guard in the early seventies, I seriously doubt the authenticity of the purported "documents" regarding the National Guard record of George Bush.
That's it. It's just possible they could have had an IBM Executive typewriter. It's just possible it produced proportional spacing exactly equal to that in Microsoft Word. It's just possible Killian used this elaborate typewriter to write a CYA memo to himself. It's just possible he forgot standard military abbreviations. It's just possible he could have used the word 'feedback' in its 1990's sense.
All of these things are barely possible, on their own. But put them all together, and the answer comes out 'BS'. Or maybe "CBS'.