L31MaxExpress
I'm Awesome
L31MaxExpress' point was that any Chevy head can make 350 hp. I think your engine builder was talking in generalities when he said "300 hp head".
As for the rest of the conversation, it's all the Theory of Constraints. When it comes to low end torque, the head matters less because you're not maxing the flow out. At a high rpm the flow through your heads is the constraint, but at a lower rpm the heads can flow plenty and the camshaft is the constraint. However, if you maximize the camshaft for low rpm torque the camshaft can become the constraint at high rpm.
Exactly at lower rpm there is more time for the cylinder to fill.