I,m putting vortec heads on my early 350 sb. looking for cam sugjestions. The engine has flat tops with 4 valve reliefs and a performer rpm manifold and edelbrock performer carb. The car is a 53 chevy with a new process 3 speed overdrive with probably a 3.50 or 3.77 rear axle. compression chart says about 9.4 to one. called comp cams and tec suggested the magnum 270, also he said I could use stock springs and retainers. Lift is 470 durationaround 220. wondering if I can go a step up on valve springs that will go on heads without any machining. read a lot about what you should or shouldnt do would like to hear from some one who has done it.also is anyone running a magnum 270. thanks Jim