I am running a 78 440 in my pickup. Right now it has 516 heads on it, a cam of unknown origin,( perhaps it's an rv cam) and it runs fine. I am about to pull the engine to replace some seals and swap in a fresh Summit #6400 cam that is 214/224 duration at .050, with a lift of .445/.466. Basically a factory style Magnum cam. I've heard that I would be better off using an open chamber 452 head, rather than using the 516. The engine is a low mileage motor home mill with the low comp pistons. I would appreciate constructive thoughts on this. Thanks.