Camshafts only go half engine speed, they are relatively light and a relatively small in diameter.
This all reduces the impact of being out of balance.
Also valve spring pressures set up their own out of balance forces.
A small block Chevy V8 is out of balance by design.
I never analysed anything else, I expect in line and horizontal engines of 2 or more cylinders should be in balance by design, and any out of balance due to manufacturing tolerances would be very small.
All in all I see very little potential for gain by counter weighting a V layout cam and even less by balancing an in line or horizontal engine.
Regards
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