This is stepping into another controversial subject.
But, I will.
A balance tube only helps idle if the carbs are out of adjustment by equalizing the manifold vacuum in 1-2 and 3-4. It does nothing at low manifold vacuum. My car originally came with Hitachi Strombergs bolted right to the head. Now they have rubber isolated float bowls so no fuel frothing.
It ran fine then circa 1986.
When I ported and polished my cylinder head, I drilled through the head vacuum port all the way through and epoxied in a 1/2" hard copper tube. That is my balance tube. I did it because I believed the truism, (it needs a balance tube). Since I smoothed everything out in the port, it does not interrupt the flow very much.
That as 1988 and it has been in there ever since and no leaks. jb weld is great stuff.
My car runs great. No issues.
Anyway, in my opinion, a badly done balance tube will do more to hurt performance than it will improve idle.
I have said it before here, I would try it without a balance tube. Just for reference, twin dcoe webers (4 chokes) don't have balance tubes. The manifold vacuum between the front and back carbs can be different as can between 1 and 2 and 3 and 4.