All that advice is well and good. I won't use the prop.
I can see that I have compromised the structural integrity, and the safety of the thing.

The reason I posted in the first place is because I did not want to have to do this.
As you can see from my photo, the prop was not heavy on one blade or another, it was heavy 60 degrees from one of the blades.
I don't think there is any good way to balance this prop after it has been drilled.

In the future I will try opposing the piston ... but I think all good engines have a counterweight that does that already.

Ken