once again we must first see which heads you are useing, what exactly you want this thing to do and when (cruising rpm, is it gonna see the local track, hp expectations) now be realistic with this part we definatly can't make 1000hp on pump gas for $1000, what exactly you are willing to change, how much $$$$ you are willing to dump into your toy, and last but not least how comfortable are you with your own mechanical abilities. if you can answer these questions it will illiminate a lot of needless information for you.
there is a guy here in the us that has proven 700+ hp with stock iron heads that he ports. it's out here it all resorts back to the above questions if you could answer them we could probably help you out.