it is all ways better to use cid to get tq .it will take alot to get500 hp out of a 396 with pump gas but 420 hp would be more realist .and you would not cost so much but at this point it still would need some money spent in the rigth place. first would be a small roller cam and head work you need to find a set of heads that will give you the most cr because the pistons are not cheap for the 396 so a set of small dome 325 hp pistons and close chamber heads would help on this.I have bulit some 396-402 a good small big block and can be made to run but it would be easer to build a 496 cast crank and hiper pistons for about the same money and make more hp and tq on pump