It ain't vast, it's just old. :-)
Somewhere along this trail, Master Oil Team & Wayne B. settled into my understanding.
So, Wayne; the Title is true, I was there during a transition time for outboard and moto GP racing (and others similar);... and was trying to gain knowledge. The journalist coverage of the era and much supporting details was very well done. So I read it, remember it because of timely correct details, and eventually it all becomes Old Information. The problem of not remembering this many decades past of stuff that sort of no longer matters certainly does not merit a "wealth of knowledge" characterization. Only maybe a decade later you active folks gathered your own very worthy history & a complete set of advancing details.
My oldest vague memories of rotary valve published information are so muddled that to comment on the disc rotary valve concept or its first use would be bogus. I am not at all sure why this old thought pops up but here goes. It could easily be wrong. The Isle of Mann moto-GP races up through the very early 1960's had a 50cc class winner one year manufactured by Kreidler of Germany, (not sure of the spelling). The motor was, I think, a single cyl., disk rotary valve type and showed quite a power advantage. It also had a secondary "overdrive" type gear system so had 12 gear ratios fit the power to that odd hilly road course. I recall listening to the sound records of that race in Jim Dunn's basement with the Kreidler accelerating out of the slowest corner and shifting up almost endlessly. The rider interview later was fun as he (Anscheit?) was saying, "Ya, mit de hand and mit de foot ve make 12 gears".
The oldest diagrams of rotary valves I recall were cylindrical and used for industrial applications where external "supercharging" was operating so exhaust ports & inlet ports/passages needed to be sealed at particular times.
As for the disk rotary valve; If the German fellow you mentioned, Zimmerman, was part of that Kreidler motorcycle factory team then he certainly would be a candidate for all following applications of disk rotary valves.
I doubt that this helps much with your question but maybe it provides some old leading information to track.
Russ R.