small block LA 600 Hp set up

Step 1. Get the BEST heads you can afford.
Step 2. Proceed from there.
100% absolutely agree! That way the heads will not be the limiting factor. I have read and seen that for a small block normally aspirated engine, the maximum HP will be about 2X the intake flow at 0.500. There have been some exceptions, of course, but it's a good rule of thumb.