Neutral balancing a 360?

I'm not talking internal balance like with a 273 - 340, the engine would still be externally balanced but with a different flex plate that would allow it to be run with a regular (unweighted) torque converter.Anyone ever heard of this? The shop doing my 360 says it works good. He showed me the flex plate he uses, it has a large scallop shaped area cut out of the side opposite to where the weight is welded on. Claims it results in a better balanced engine b/c using a weighted TC to balance it the "conventional" way isn't as accurate due to the TC not being filled with fluid during the balancing operation.