The engine in my car started as a completely stock '71 440 spec short block.

With (unported) Eddy heads, performer RPM intake, and a slight upgrade to one of the comp cams xtreme camshafts (it's around 0.490 lift, IIRC) it made about 470 on the dyno. That was at about 9.5:1 compression.

With a tad more compression, and just a little more cam, 500 hp is pretty easy.