The offset is indeed on the flexplate, because the 6 bolt pattern on the crankshaft is asymmetrical.
Flexplate only goes one way.

This was almost an admission of several decades of engineering oversight....

In hindsight, flexplates could have been made balanced in 1973 because of the crank bolt pattern, but were not.
Instead the weight was added to the converter and the converter also had asymmetrical bolt pattern.
The complexity and slightly increased difficulty of assembly and service was really unnecessary, they could have done all cast cranks the same as a 2001 5.9 magnum all along
if they'd figured it out sooner.

Once the flexplate contains the imbalance, then the converter can be built to neurtral and bolted on in any of the 4 positions.