How can I tell if my engine is balanced

[sd_iconoclast]

I am increasing the displacent of my '88 Fiero engine by using 3100 block that has been overbored to 3400 diameter (sonic testing showed plenty of meat).
I am using DOHC pistons as is recommended in the build thead in the "Engine swaps" section.
When I picked up all my parts at the machine shop, I asked the machinest why I had not been charged for balancing as I had specified the parts be balanced.
He said that I did not need it. He said that he had weighed my pistons and rods and they were within spec. He said that balancing is not needed when you stay with factory pistons. I pointed out that I was using DOHC pistons instead of 3100 pistons. He repeated that he had weighed them and they were the same weight as the 3100 pistons. I also asked if it was significant that I was using a 3100 crank and fiero flywheel. All the fiero flywheels I have seen have a bunch of holed drilled in them on one side. I understand that these flyweels are neutral balanced, so why do they need all the holes?
How can I tell if my engine is balanced or not?

[sharkey]

the flywheels need the holes for balancing. when the flywheel is cast, it has heavy spots, so to counter that, they drill holes in it to lighten that spot till its neutral balanced.

[geoffinbc]

Good pistons often come within just a few grams of each other so they don't need adjustment. But he should have balanced the crank with bob weights after he weighed each big end with the bearings in them. Ask him if he did. That is a real balace job.