500 rwhp is a tall order from a 351 w!!! you will have to have 12 to 1 compression ratio minimum, big solid roller and the 205 heads. Those pistons look stock is that pic @ tdc?? if it is you will definatly need to think about different pistons. that deck height looks pretty big. the size of your cam will determine if you need to get valve relif's fly cut into the pistons.
good luck
good luck