It depends more on if they are stud mount or pedistal mount and spring diameter. Which heads do you have exactly? X303 or X305? Summit says the X303s come with guide plates which would leave me to believe they are stud mount, and the X305s dont come with guide plates, so I would think they are pedistal mount. But both are listed as using bolt on rockers so its hard to tell without takin off the valve cover and checking.