I mean when you had your cylinders ported,they raised the port roofs,if you use a spacer it will raise them even higher. If you throw the kit together with no additional porting,it will run,but it may not be optimal. Sometimes port jobs can be changed to work with 4mill cranks to make it right,sometimes they cant. Before i spent 700,have your cylinders looked at and find out exactly where your height and durations are,then someone who knows about porting can tell you exactly the right way