400s have same rod/stroke as 383 but much bigger piston. 440 has longer stroke/bigger piston than 383. Plus factory balance is pretty loose. If you already have wrong balancer and a vibration I would go ahead an try the other 400/440 balancer all you would be out is your time, because like you said its already wrong.

1973 Charger, former SE, former auto

I'm not trying to be difficult, it comes naturally....