I would agree with this comment, however I made nearly 430hp with small valve, iron "J" heads and a relatively mild hydraulic cam. If I had gone a bit more aggressive versus conservative on my cam choice, it would have made a better number. There was allot left on the table but still a very respectable, reliable daily driver number.
Heads is absolutely the key in these engines but my example shows you can make well over 400hp on a budget.