FINAL UPDATE - PROBLEM SOLVED
Ok. So after replacing the entire fuel system, the problem was where we first started - the governor flyweight sticking.
NB. For future reference, see my earlier video of the engine running with the throttle plate off so the governor fingers are visible (
). My original questions in pursuing the governor were to see if anyone knew if the movement of the governor fingers should be noticeable. I wasn't sure if the governor adjusting the throttle slide would be big enough to see it move if it was just making very minor adjustments to the slide.
I would now suggest that if you don't see the fingers move under changing load conditions, you should head to the governor flyweight first.
I have no regrets in replacing and repairing the entire fuel system along the way. Everything that was repaired or replaced was in terrible condition and I couldn't believe it was running at all in the condition they were in.
Thank you to all for your input along the way. It's been a great education.
Let me know if you have any questions about the process.