You need a convertor w/ the balancing weights for the cast crank, a convertor w/ weight welded on, or the B&M weighted flexplate that lets you run any convertor for a internal balance engine. The B&M gives you better flexiblilty for the future and last I knew they weren't real spendy.

'69 Road Runner 383 going to 440, 6brl hood, likely gonna race it '70 Challenger R/T clone 440, 2nd owner, 300,00 miles on body, not kidding '92 Cummins 1 ton, in need of restoration bad '79 360 1 ton flatbed-for sale '01 WS6 T/A- for sale