If your goal is 900 hp in the future, the cheapest route is to start with those parts. You can do it with B1 heads, or 572-13 heads, or even 440-1 heads. But the latter is going to require that you have all the tricks to get there. that equals $$$. My cheapest recipe would be to locate a used set of B1 heads that flow well ( good porting work) and put them on a 540 557 or 572 shortblock. The deal won't have to be real exotic to get 900 hp.