Balancing cast crank 340

If the rotating assembly is going to be rebalanced, it doesn't matter what the replacement pistons weigh because the balancing job will adjust for it. Hopefully the newer ones will be lighter and some weight can be taken out of the crank counterweights. Anytime non-OEM parts start getting swapped around, you need to rebalance, so a 318 cast crank can be made to work. OEM balance jobs weren't that accurate anyway.

I agree with the B&M flexplate for a cast crank 340 suggestion. It's stronger, much simpler and not much more expensive after getting the weights and then welding them on the converter.

340 cast crank counterweights are the lightest.
360 Magnums are the next heaviest.
Original 360's take the most weight.
(The newest B&M flex plates will have weight taken out of the opposite side as opposed to weight being added.)

I have a balance kit somewhere with more details. I just can't find it at the moment.