your 408 with iron heads IS respectable at 430 hp. But it is under headed for any future big hp gains.
If I'm building an engine and need to sink money into refurbishing heads, I'm moving to aluminum for a few more bucks.
Only because i can work the heads myself and measure the improvements on my own bench am i not hitting the full on agree button. lol
But i hear you... and if some dont even have a decent set to start with, especially...then why not buy aluminum. They're like 300 each anymore and even cheaper name heads do better .350-.550 flow than a stocker as cast.
Definitely agree the 430 hp is respectable.. yet no more room without substantial work to them or a better head.