Back in the late 80's I had a 426 Hemi that wouldn't idle properly with the stock Street Hemi intake. A rough vacuum leak type of idle with a mild hesitation.

The engine was built to stock specs with a 70-70 stock Hemi hydraulic cam so it should have idled smoothly.

The carbs were freshly rebuilt (professionally) and it acted like it had a vacuum leak at idle.

I checked for all the normal gasket leaks and couldn't find any.

Someone told me to check the floor of the intake for possible small holes (porosity or corrosion) in the floor of the intake that would go into the exhaust crossover.

I pulled the carbs off and saw a dark spot like carbon on the intake floor.
I pressed it lightly with an ice pick and it went straight through into the exhaust crossover.
I wasn't running the heat tubes on the car.

I had the area welded up and the car idled perfectly after that.
Vacuum leak fixed!

That may be your problem or it may not.
You would just have to pull the carbs and to inspect the intake floor to know for sure.