Forgive me, I'm new the the world of MB but this seems backwards to what my prior engine experiences have been. The mopar 360 v8 for example is externally balanced and has weights added to the torque converter to put the engine in balance. The same torque converter can be used on an internally balanced 318 engine if you remove the added weights (thus making the TC neutrally balanced)
My interpretation of internally balanced is the the crank counterweights are "adjusted" to provide balance and the flywheel and balancer are "zero balanced" (neutral). Externally balanced means that the crank is not fully balanced on its own and requires counter-acting balance of the flywheel and damper to put the whole assembly into balance.
Again, I'm just trying to get this straight.