Not to be a contrarian but Angel shot voicing on only one string groove would not be recommended unless you want to redo the hammer string mating. Where to voice will depend on where the hammer is hard and how deep. You can only determine that by listening at various dynamic levels. Blue points can require some aggressive radial needling (all the way around the hammer, deeper in the lower and upper shoulders and backing off on or near the crown. If the hammers have been needled to the point of showing craters the voicing will not likely last because the felt has been compromised. You are essentially just fluffing up layers that will likely pack back down with a minimal amount of playing. Time to explore a replacement hammer and do some sampling with something softer (like Ronsen Wurzen--my general preference for that piano, or Weickert or even Ronsen Bacon felt). Sometimes the Blue Points are simply too hard for that piano.I would NOT install riblets until you've sampled another and softer hammer. That's not the proper use for riblets, IMO.