Eddies Vs 915 J's

With what you mention as cam size, and a rough idea of the RPM's mid-lift abilities - I feel confident saying you can eclipse the 400hp mark with a maxrpm of 7K. Peak power will be lower than 7, but so will your total output be lower than it could be with a larger cam. I don't think 450 will come with the lower end you have. Especially given the need to customize the pistons to work with them. If you had a clean slate, could run a flat top, high static ratio, a tight chamber, etc etc etc, then yes. I think it's doable with enough cam and compression. But not with what you have as a shortblock. I also think the compromise with adding the heads will be loss of some lower end torque. You will make more power at peak torque - but it will be a more peaky power curve, and pushed up in the rpm band from where it is now. The car will still feel faster - the heads take a bunch of weight right off the tallest point over the front wheels.