Call, and talk to Drew at street and strip performance, here in Louisville, Ky (502) 969 1500. I had a similar problem a few years back with a 340 cast crank flex plate. He's been drag racing Mopars for 30 years plus. I'm sure he can help you. I'm almost certain that a cast crank 340 uses a neutral balance flex plate as well. Because the torque converter is the balancing end of the crank. As the externally balanced harmonic balancer does the front end. But call to make sure.
