The HRs are poly, and come it two hardnesses. May or may not change vibration in the car, depends on who you talk to. The softer one should be good for street use. Some people put the HR mount on the drivers side, and use a stock type mount from Pioneer, or other vendor, on the passenger side. That stops the engine from moving around, with less chance of noticeable vibration. As far as engine height goes, I think they sag as they get old, so even if you use OEM mounts, when you replace old mounts, the engine can be higher.