Torque converter

I guess I don't understand this neutral balance thing, aren't all converters balanced.

Yes. Neutral balance means the converter is balanced as is with no weights added for an externally balanced engine. Converters made for externally balanced engines have weights welded to them.

The exception is when you use a flex plate that is made for an externally balanced engine. Then, you can run a neutral balanced converter on an externally balanced engine, because the difference is made up in the flex plate.