Cracked Flex Plate

I am beginning to wonder if the reason the flex plate cracked is because the transmission builder failed to install the bushing in the front pump to hold the converter centered. Otherwise I am unsure of what would cause the flex plate to crack in the first place. Are they that weak behind a little 340 that is not built? If that bushing was not installed, then the converter is only centered by the flex plate and it is going to flop around until the flex plate cracks, and then it really starts to move. The neck of the converter I removed was a little scored, but not that much.