ATI super damper?

PRH said

I believe all the Speed Pro flat top pistons would be pretty close in weight to factory pistons.

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If thats the case, then its probably that custom flywheel that wasnt balanced to the external balance specs of a cast crank 440. That's about the easiest option he has, remove the flywheel and have it balanced to a stock cast 440 flywheel spec like this one

Somewhere there is a weight kit for a convertor but it may have the balance specs for this operation
Mopar Performance P4120241 Mopar Performance Balance and Positioning Template Packages | Summit Racing