[johnneilson]

Interesting inquiry, I found old picture of B-B counterweight drawing some years ago.
I then modeled up in solidworks, from a pretty bad sketch.

I come up with mass of #4.87 per counterweight.

As an interesting side note, the Miller racing engines found that you could not get enough counter weight to balance out the harmonics. If you look at pics of them, the counterweight is full radius and 180 degrees opposite the rod journal.

John