i am building (retrofitting) a set of Magnum heads onto a 1967 318. I am doing all the custom work on them, and have a question about the rockers. I am maxing out at .500 lift and no more than 6500 rpm (planned shift point is 6000-6200). Are the factory rockers up to that? I never had a question about the shaft mounted ones. A conversion kit for the serious racers is about 400 bucks plus tapping for bigger studs. I am wondering if it is needed for my somewhat mild setup. Anyone have experience with these in that regard?