Still can’t figure out the 318 is the nearly the same as a 340? A 318 responds to a cam as any motor near the same cu in. Horsepower is related to airflow through the heads. It does not matter what size the ports are, just how much they flow. You can get there with 340 heads, ported heads, Magnum heads, aftermarket heads. It all boils down to what you want and the combination to get there. In this thread people have given combinations that will get you 340 horsepower and time slips.