You are probably right. I was basing that on the fact that my mildly modified 340 with an Air Gap, 750 CFM carb, XE 268 cam and headers is at 370 HP. That is about 1.09 HP/CI. So with the OPs better heads and more cubes, I guessed 450. More cam might be a better choice, and the 268 might not make 450, but I bet it would not be Too much under that.
You are absolutely right. I think that is why most of us are adding that caveat.