I believe you're shooting your self in the foot going with a 318 in that heavy of a beast and that your horsepower expectations are unreasonable. I would highly suggest as mentioned to start with a 360 at the bare minimum plus the 4" stroker crank would be much better (cheap cast cast is fine after checking it out) or maybe a better cast crank. I can guarantee if you could ahead of time evision the different results you'll end up with between the two that you would not regret your decision (to forget the 318). Good luck with it & holler later on how it goes (& in between with any Q's)