OK, thanks Charlie, I appreciate your speaking up. I was going by the old Performance book. It says explicitly that they are not interchangeable. And since there are other incompatible differences between cast and forged cranks, I would be hesitant to swap the dampers too.
It may be that the damping ring itself has a different weight between the 2, and each is made to dampen the internal crank vibrations in a certain RPM range with certain weight in the crank, and each is optimized for the 2 different cranks. (No, I am not referring to throw weights and such, which are all balanced out internally as you say....) Interesting that the different trans would actually change the damper....perhaps again it is the rotational weights at the ends of the crank.