340 idle problems

Why so far from stock parameters... Because the stock parameters were for a multitude of reasons other than max performance.

IMHO, when you build this stuff, don't pay one bit of attention to stock settings for timing, idle, carb adjustments. They are pretty much worthless if you want the car to run properly.

Let the car tell you what it wants with the tools you have available. That's the best way to go about any tuning adventure.