RE: Balance system
It evolved as a cheaper alternative to a solid metal plate because the heavy stabilizer ring at the top of the tub was filled with steel filings which were essentially factory waste while the early harmonizer was a cast piece of metal.
In 2001 John and I transported a tub for a WO-65. We put it in the van on its side. BIG NO-NO. The filings shifted and the first time Robert went to use it, the unbalanced dynamic forces almost took out half of Minneapolis.