With stock flow in the upper 240-250+ range, it would be big stretch to get the HP you desire...even to get 500hp, while doable, would take quite a bit of cam to get there.

for whatever it's worth, a generic formula that applies only to 8 cylinder engines is that for every cfm of flow, a head can support 2.05 hp. IE, heads that flow 250 cfm can support as much as 512.5 hp...and that really doesn't change whether it's a stroker or not...the peak rpm and torque changes though.

As stated, a set of professionaly ported eddies can do the trick.