Vibrations / Shaking / low power
I say BS. An out of balance converter will indeed make an engine vibrate BUT NOT ALL THAT BADLY. I once ran a 360 with a 340 flywheel and other than NOTICABLE vibrations at SOME RPM it wasn't earth shuddering NOR DID IT cause real loss of power.
NOTE:!!!!
This was way WAY before Al Gore invented the internet