I am no guru. But the golden rule of tuning is you always set your timing first and you never tune the carb and change the timing at the same time. You need to know what the total timing is for the engine, and if you have the base timing that's good too. You ignore the carb quirks as much as you can and get your initial and total timing set first and lock it down. Then you can start adjusting the carb and if that means you have to adjust the idle screw beyond .020 then do it. If that adjustment then induces a stumble, then fix it in the carb, not by adjusting the timing. If the car won't idle below 26 degrees, fix it in the carb, not by going back and advancing the timing. That engine should idle well below 26 initial.
I suggest you spend $10 and buy
Don Gould's "Tuning to Win" eBook. No affiliation, other than its the best $10 I ever spent and taught me how to tune carbs and diagnose problems.
EDIT>>One other item, if this is a double pumper with mechanical secondaries, you should approach the carburetor as "square" and make equal adjustments to front and rear at the same time. Primary and secondary jetting should be square, both pump lever arms adjusted equally and both transition slots set identically.