408 small block street build

When i built the motor i wasnt looking for big hp (600ish) i got the indys fairly cheap in the kit.
Obviously some track time here would be of most value but i know of 2 other cars here in adelaide with back to back dyno figures with considerable losses.
720-515hp
605-394hp
But i tend to agree mine is probably lingering around the 450 mark especially because it seems to have the go down low.

Without doing the obv of cnc ports big cam and big comp.
What sorta suggestions for maybe getting it up to 500hp or 520.
Worth getting the heads flow tested as is or get them ported even without big cam and comp ??
59cc chambers atm so probably wont get the comp up much more without pistons .