Internally balanced?
If you'll notice on our cars, there is no indexing pin or offset bolt circle like an American V8, meaning it can be oriented in any direction. This is usually a sign that each part is balanced individually. Some fly-by-night shops that treat the L series like a V8 however are sometimes tempted to re-balance by taking material out of the flywheel. That said you should be fine just swapping your flywheels, but if the motor is apart, getting the bottom end balanced is always a good idea.