I've got to determine the pushrod length on a Pontiac motor and I'm not sure what to do. I know you run the cam to mid-lift and make sure the rocker is 90° to the valve stem and the roller centerlines match up. My problem is, I'm using a skid ball rocker with a roller tip and I'm not sure where the skid ball centerline is. Im thinking it would be at the top of the ball/base of the polylock. Any suggestions? Thanks in advance.