I think I can answer your questions.
[1] The holes in the front of the choke housing is for bypass air. Earlier TQs had a passage in the baseplate. There was a notch in the top & one in the bottom of the BP. If BP air was needed, there would be an interconnecting hole drilled. So air was routed from above the t/blade [ at idle ] to below the t/blade. With this setup, high idle speed could induce nozzle drip. I believe these notches is what causes the whistle with some TQs, not air being drawn past the shaft. The holes in the choke hsg bypass the t/bores & avoids possible n/drip. Those holes should only be blocked if the t/blade to transfer slot gap is too low, which would be unlikely.
[2] Brass restriction. Is it the one the A/valve plugs into, carb rear, pass side? This reduces the release rate of the AV. Might be used on the 850 if used on smaller engine, like a 360. Maybe for emissions, not sure?
[3] The extra threads on the mixture screws are so that you have enough adjustment with the finer taper.
