An update (about 6 weeks after install): While the vibrations did get better, the 'drone' at 1500 rpms was very annoying. And it would make a buzz in the dash somewhere too. The vibrations were enough that new passengers would comment. I read somewhere that the later SHO's don't even have the front mount. With that in mind, I went back to the stock front mount (which is still in very good shape). I'd say that about half or more of the vibration is gone. I believe I still have all/most of the benefit from the just the rear, with very little of the downside.