The Indy Rockers are extruded Aluminum. I didn't know that until I did a little research. The same company that makes the TD Rockers makes them for Hughes so they say. I didn't get the Cryo treated rockers and I don't know the spring pressure but Larry Smith put the new springs on the heads and said they would handle just about any cam I wanted to put in. I don't know about longevity of the rockers but I do like the way Hughes does business.