IMO putting metal blocks instead of rubber or poly mounts is a bad idea. The main reason that they are made out of rubber is to absorb some of the resonance and energy coming from the metal going into another metal. If is better than we should also all run metal rods instead of struts and springs. I guess I don't understand how metal could be softer than poly or rubber to cause less vibration?
I would make your own solid mounts out of fluid filled stock mounts from the auto parts store. You can fill them with either poly or black RTV you just have to decide what shore rating (hardness) you want.
As far as vibration with poly uppers or solid lowers....It is almost a must to adjust your idle RPMs up higher. The stock setting is pretty low and doesn't account for the harder mounts.
