It’s not worth trying to run it as is or with a corresponding chunk 180 deg opposite, unless you are willing to drill holes here-there-everywhere in an effort to balance it (using what for a balancing tool ?).
The vibration from an unbalanced flywheel will put stress on the crank, rods, and crank / rod bearings.
I have seen snapped rods and crankshafts from unbalanced flywheels.