At home flywheel balance....

In my humble opinion, the open bearing with big balls may not be suitable for the task.

If it were me, I would set up some strain sensors along with a position reference sensor. I would use a micro controller to read sensor signals, and determine where to take weight off. I would then verify, to insure correct balance.

In engines I work with the crank is balanced with flywheel mated.

How many grams do you think I would need to add to the opposite side of where the plasticine is ,to change the position of the flywheel?