From reading all you have done and considering the symptoms you have described I would be having a look at the valve train.
Your symptoms point toward fuel delivery issues, but if you are adamant the carb is fine then move on to the next system.
You said it sits idling for hours just fine, then when you start to work it it goes down hill.
Only two things are changing;
1- Need for more fuel.
2- Increase in operating temperature.
Strange things can happen when components of the valve train are worn to the limits.
Expansion of components when hot can change clearances just enough to prevent a valve from fully seating, as well once the oil is hot the proper operation of the hydraulic lifters can be marginally impacted.
If for example an exhaust valve is not fully sealing when hot, the piston will not be able to draw sufficient fuel into the cylinder on the down stroke, your action of closing the choke creates a restriction of the air flow which allows more fuel to be drawn through the jet getting you back to the shop.
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