It is my understanding that those type of B&M flex plates (half moon, cookie with a bite out of it, etc.) provide the balance due to the cut-out. When using that flex plate you want to use a neutrally balanced converter, NOT a 360 converter with weights for balancing.
What you're saying is use a 360 converter with weights AND that B&M flex plate? That defeats the purpose and will throw off the balancing.
