i dont know how street-able the 500+ HP small blocks are. RB would be the way to go to get that kind of power and be a little more mild mannered.

are you looking to do this naturally aspirated? i looked into building a small block and after thinking it out went RB instead. parts and labor are basically the same, and my thinking was to have a motor that was not "maxed out" so i could have room to upgrade in the future if i wanted to.