Hope you are enjoying your SB3. We sail ours out of Newport RI and like the boat alot. My spin blocks came attached with small u shackles and have never come off. You can get them at any marine store. Our keel vibrates at planning speed. I'm not sure what you can do but it is the sound of speed! There is a tuning guide on the uk sbs site and class forum with lots of good stuff. We race with Newport Sportboats (phrf) and enjoy competeing with an open 530, mx20, two vipers, and sometimes other sportboats. We race at 120 phrf. If you cant find the tuning guide I can mail it to you. If you are ever up this way with your boat feel free to race with us.  Regards, Scott 3480 Jester.