tufcj wroteOEM stuff was generically balanced based on the average weight of crank, rods, and pistons.
Close enough. If the factory could sell replacement flywheels over the counter that could be bolted on and go, it can still be done. The are thousands of flywheels sold every year for Chevrolets, Fords, MoPars and every other make for engines that are not neutral balanced and they work. Engine balancing is compromised on averages anyway.