i have a 302 that i have spent a little over $2,000 on and i have done everthign and anything you can thinks of. everything is new, bored, or rebuilt. the onlything that i didnt get for it is the heads. well i rebuilt them but once i got the engine running the thing ran like crap. it only runs on 4 cylinders. i was wondering if the casting numbers on the heads are supposed to match up? the codes on mine do not. if you are looking at my engine from the front of the car, the right head seems like a 351 head. the rocker arms clap and there is about a 1/4 inch from the spring to the rocker arm. can any one help me?