I saw you said off roading does this mean you have a 4x4? Popajohn is right cleveland heads make power higher up in the RPMs. Instead of a cleveland intake just spend the 189 dollars at summit or jegs for the Weiand intake manifold for 351M/400 engines. Its a really good manifold. Now whats your truck gonna be used for? You could still use the cleveland heads cause its will bump up your compression ratio which is serverly needed on these engines and you make some power down low it will just really throw the power on a little bit higher.