Transmission yolks: difference between C4 and AOD?

I'm swaping my C4 out for an AOD and I need help understanding the differences between the two yolks. The AOD, which came from an '88 Lincoln Mark VII, has what looks like a harmonic dampner on it. Is this needed for the AOD? or is it only used when using the Lincoln driveshaft. II prefer to use the original '66 driveshaft.

I will be installing the AOD this week and will check to make sure I still have about 1" of play between the yolk and the tailshaft.
 
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