... Um...
Okay it sounds like you have indeed gotten a bad deal on this thing.
If the engine builder actually said to just go ahead and try the different weights then he is a f____ng moron and you need to find a new engine builder, I don't care how well known of a mopar guy he is.

Your best starting place in my opinion if he claims the balance guy said it was good where it was, would be to remove the offset balance flexplate and bolt on a neutral one along with the neutral balance converter.