I know a lot of engine builders do the forged internals to 50% on average but no do not know what stock is still trying to find the difference between a stock VG crank and the 800USD Nismo one.
It's not a matter of 'doing it to this' or 'doing it to that' which is why they call it the black art or whatever. It also has nothing to do with the crank alone, it takes into account the: weight placement the reciprocating path plus a small oscillation of the rods the rods maximum angle of inclination - bore axis the rod length and ratio the geometric center of the rods the angle between the cylinders desired RPM range tolerance of vibration amount of power developed type of engine mount engine mount attachments etc dynamic factors such as pressure acting as weight such as vacuum compression and combustion pressure piston ring and drag recripocating component motion vs direction and the list goes on.. and on.. and on.. then each detail goes into depth that I don't understand, nor would anyone on this forum, maybe not even the tt.net forum, unless you have been balancing engines all your life like the guys who told me this and from where I read some of it. The more I research into this it seems as though there is no such thing in saying "if it's balanced then, it's balanced". Another thing I have found out that there IS a need for a harmonic dampener regardless of if the crank is internally balanced or not, but again it's something for the owner to decide on. It goes into way to much detail why can't it just be simple I guess this explains why some balancers have no idea about it.
