I am building up a 402 for my 70 Chevelle SS. I have the original engine in it now but I'm afraid to push it too far and maybe blow it up. That would drop the value of the car a bunch. So I'm putting in another 402 that I picked up. What I have is a set of 3981063 heads. Are these any good for a street perfromance engine? Also what is the difference between a cast, nodular iron and a steel crank? This block has a nodular iron crank in it now.