If you are convinced the idle circuit is too lean then hone the IFR holes a .001" bigger.
Don;t get all carried away.
Give it more idle timing , first. If it runs on use a idle stop solenoid to allow the throttle to close when off.
Heavy dependancy on manifold vacuum at idle for idle advance will result in a bog when you rug it
as the idle timing disappears.
The .020" T slot pre-setting is not carved in stone. Give it what it wants. Adjust as required.