Hi Chris,
I don't have any of the engines that you listed but I have run modern marine engines - they don't seem to mind flywheels (not sure what that proves though.)

But I have an old PAW19 DS that had a full circle flywheel that used to vibrate quite badly and after grinding off the cheeks as an attempt to balance it, and it was much better.

Do you think that adding a flywheel makes this better or worse?