@wrm57 When we talk about tonearm resonance and damping nobody is thinking about a resonating counterweight aside from the fact that thin coatings do not do much.
As for Long Arms, Schroder will not make an arm longer than 11" He feels that is maxed out and I will defer to him on this. It is certainly a lighter arm to begin with and you have the flexibility of using a variety of cartridge mounting plates. I only use 9" arms not that I have much choice as that is as long as my table will take.