"only 400-450hp"?!?! lol
You can get to 400hp with slightly modified vortec heads and an aggressive cam, but its not going to be great. The cheapest way to get to 400-450hp is with a good cylinder head, and the best value you are likely to get will be some AFR enforcer heads. You can get some ones form Skip white that have good components for about $1100. They also have smaller chambers that will bump your compression up enough to get to your power goal with a reasonable cam that will be actually drivable in a truck. The vortec style replacements with some decent flow improvements are iron and ~$700, so for the price difference you are much better off with the AFR's.