5.9 Magnum to replace Older 360, flexplate?

Can somebody explain the relationship between internally balanced engines and externally balanced engines and the torque converter having a weight or not? Here we are saying remove the weight for the 360 Magnum, as it needs a neutral balance torque converter, but I thought the weight on a torque converter was to rotationally balance it in the first place. What am I missing? Thanks all.