Frank, In looking at it again, and "playing" with it, I concur that it’s set up correctly,
but it was a little out of adjustment.
I ran it for a little bit 1/2 hour before I took the video, and it idled
a lot slower. Determined this morning that the throttle butterfly was not shutting
all the way, and suppose that one of the trunions slipped a little.
I now have it so it works smooth, and goes fully open and closed. Have
not run it yet, as it was raining. Peeks of sun coming out, so maybe later today.
Anyway, from what you said about the "intent" of the setup, etc., and
from me playing with it, I believe it’s working correctly now, and note that……

At Full spark advance on the mag plate, there is full throttle control, from
idle to fast on the twist grip. As the spark advance is reduced, the setup
limits the throttle opening, which make sense.

Interesting answers so far on the trivia question!
Thanks.