No Lift 360 Swap Tips/Suggestions

Check your 74 converter that it has no big weights, in other words, that it is actually from a 318 and NOT externally balanced. If my memory is correct, the flex only bolts to the crank in one position, and this should be the weight you need for the magnum. The elongated hole I don't believe matters, but that is an easy matter of trial bolting it to the converter and marking the hole to be "done."