440 crankshaft questions.... Pic included

Ok so I am fighting with my 440 right now. Not sure what to call it, but I can't remember seeing this rear piece with a notch cut out like that.... I was told that I have a cast crank and that I will either need a counter balanced converter, or the flex plate that B&M makes. I went for the flex plate so I can run the neutral balanced converter I already have.

What can you guys tell me about this before I go to stabbing the transmission back in with this flexplate?


Thanks in advance