RE: Spinner bolts break
The 70 flight changeout might be a good idea. If you stop and think about it, the speinner bolt is fairly long, and is normally cantilevered out quite a bit. Do you balance your spinners carefully? Harmonics will do serious damage to pieces of metal. I have not computed at what order of harmonics the spinner bolt would vibrate, but it's probably pretty far up in the order of things, and the juncture of the adaptor nut and the unsupported part of the bolt would be just about at that place. I don't think that using a hardened bolt is the answer, so I'd say change it out before it fails.
Bill, Waco Brother #1